Android 18 is originally a Human named Lazuli, and the elder out of her and her twin brother Lapis (the eventual Android 17). The twins were notorious delinquents, who Dr. Gero would meet by chance while looking for fresh material for his experiments. He then kidnapped them and restructured them into Android 18 and Android 17. She is the second artificial human, between her and her twin brother, designed by Dr. Gero to be created by fitting a human being with both biomechanical and cybernetic enhancements. The biomechanical enhancements are organic substances patterned after human cells, which makes it possible for Cell to merge with the androids at a cellular level. Gero's experiments on her do not impede her ability to reproduce, as evidenced by her giving birth to a healthy daughter, Marron. Since they are human-based, she and her brother can become stronger if they train. Though they do not need to eat, they do need to hydrate. Also, their cells deteriorate slowly, so they age slowly too
When Dr. Gero arrives at his laboratory (after he and Android 19 fail to combat the Z Fighters, with 19 getting killed by Vegeta), he activates Android 17 and Android 18. There is another android yet to be activated, Android 16. Android 17 and Android 18 want to activate him but Dr. Gero refuses. Android 17punches Gero's chest, decapitates him, and squashes his head. They eventually activate Android 16 and pursue their quest to find Goku. They are confronted by the Z Fighters, and Android 18 fights Super Saiyan Vegeta. Through the battle, Vegeta continues to lose stamina, while Android 18 continues to fight, and she eventually gains the upper hand and breaks his arm. The others try to help but are easily defeated, with the assistance of Android 17, As persistent as Vegeta is, he is no match for Android 18. Android 18 gives Vegeta a rough beating and ends the fight by breaking his other arm. The androids approach Krillin, but have no interest in killing him and Android 18 even says goodbye in a flirtatious manner. When the androids tell Krillin that they are searching for Goku, Krillin tries to persuade them to drop their search for him, but they do not listen. Android 18 goes over to kiss the terrified Krillin on the cheek before continuing their quest to find Goku then bids him farewell stating that she would see him real soon in the same flirtatious manner as before. This is when Krillin begins to fall in love with Android 18.
The androids eventually reached Goku's home. Android 18 went inside and found no one there, instead discovering a "dump" as she called it and being surprised that Goku lived there. A few days later, the androids arrive at Kame House to find Goku. Piccolo decides to take his place and leads the androids to one of the Tropical Islands west of Master Roshi's island, thinking he can now defeat the Androids thanks to his fusion with Kami.
When Imperfect Cell arrives and interrupts the fight between Piccolo and Android 17, he absorbs Android 17 and becomes Semi-Perfect Cell despite Piccolo, and later Android 16, fighting Cell. Cell attempts to absorb Android 18 as well, but he is stopped by the arrival of Tien Shinhan, who holds him off with a series of Tri-Beams so that Android 18 and the damaged Android 16 can escape. Android 18 and an injured Android 16 hide on an island where they later watch the battle between Cell and Vegeta. Krillin finds their location on the island but refuses to engage her shut-off device, which would shut her down, in spite of the serious threat that could result in Cell's perfection posed by 18 being alive. Because of this, Semi-Perfect Cell eventually defeats her andabsorbs her (with help from Vegeta) and reaches his ultimate power, easily defeating Vegeta and Future Trunks. Perfect Cell becomes overpowered byGohan (as a Super Saiyan 2) during the Cell Games, and regurgitates Android 18. Krillin immediately comes to her side and tends to her for the duration of the battle. After Super Perfect Cell is defeated at Gohan's hand, Android 18 is taken to Kami's Lookout and she wakes up. While there, she figures out that Krillin has a crush on her when Gohan yells it to everyone. This leaves Android 18 surprised and slightly flattered but too proud to admit it. She leaves but, when seeing Shenron, she hides in the lookout to see what is going on. Krillin uses the Dragon Ballsto make a wish to Shenron that Android 17 and Android 18 be restored their complete humanity, but when Shenron is unable to grant his request, Krillin takes the opportunity to wish for the self-destruct devices within Android 18 and Android 17 be removed. Revealing her presence in the process, she corrects Krillin about the relationship between herself and Android 17 as being familial instead of as lovers. Nonetheless feeling flattered, Android 18 then simply says "I'll see you later!" and leaves the lookout.
Majin Buu Saga
Android 18, who used to be a delinquent, found Krillin's seriousness and straightforwardness refreshing, and somehow or other she ended up falling for him. Seven years after the Cell Games, Android 18 and Krillin are married and have a three-year-old daughter named Marron. Android 18's family is an exceptionally ordinary household, but Android 18 is scary when she gets angry, so Krillin goes out of his way a little bit for her. When Gohan tells Android 18 and Krillin that Goku will return to Earth to enter the 25th World Martial Arts Tournament, Android 18 convinces Krillin to enter to win the prize money. When Goku returns and is reunited with his friends and family, Android 18 remains cold and distant towards him, as she is "created" specifically to kill him, and displays annoyance when Goku expresses surprise to see her with Krillin and the others, and later sarcastically says "Spare me" when Goku is even more shocked that Krillin not only married her, but had a child with her (mostly because he thinks Android 18 cannot reproduce due to being an android, not realizing that she is actually a cyborg rather than a true android). Later, she is matched against Mr. Satan in the World Martial Arts Tournament after defeating Mighty Mask (actually Goten and Trunks in disguise).
Not interested in the fame that comes with becoming the World Martial Arts Champion (and in addition, prevailing over Satan, who is generally believed by people of Satan City to be the strongest man in the world), Android 18 allows Mr. Satan to defeat her and retain his somewhat misappropriated title, provided that he reimburses her an amount of money (twice the prize money that he would be receiving as tournament champion).
After the World Tournament, she goes with the others to look for the Dragon Balls and later she takes refuge from Majin Buu at Kami's Lookout. While on the lookout, she watches the fusion of Goten and Trunks. A day later, Super Buu finds the tower and allows them to live for a short time. While on the lookout, Super Buu uses his Human Extinction Attack to kill everyone on Earth.
When Super Buu escapes the Hyperbolic Time Chamber, Krillin decides to face him alone while ordering her to leave in the meantime, Android 18 screaming out for him before he charges Super Buu, Android 18 and the others retreating into the lookout before he is killed after Super Buu turns Krillin into chocolate and eats him. Android 18 leads Videl and Bulma away from Super Buu, her daughter in hand, but is turned into chocolate along with Marron, the two being eaten by Super Buu. Her life is restored through a wish from Porunga, and she later supplies Goku with her energy to fuel a Spirit Bomb, in an effort to defeat Kid Buu. Though peace has returned, Android 18 still maintains a cool and distant attitude toward Goku (as she was originally "created" to kill him) but she still can not resist smiling when Goku returns and has a tearful reunion with his family, and smiles when Goku and Chi-Chi embrace, showing a softer side to her personality. She is later seen at a party at Bulma's house, where she playfully pushes Gohan forward to make him dance with Videl.
Ten years later, No. 18 attends the 28th World Martial Arts Tournament with her family and the other Z Fighters.
Years later, in her first appearance in Dragon Ball GT, Android 18 becomes a servant of Baby. During the battle between Goku (as a Super Saiyan 4) andBaby Vegeta, she, along with Krillin and Marron are caught in the destruction of Satan City by Baby's Super Galick Gun. However, all of them appear to have avoided the blast. She is later cured with the Sacred Water. She must later go to the Tuffle planet before the Earth explodes because of the wish by Baby to restore his home planet. Afterwards, she attends a party at Bulma's house.
Super 17 Saga
Some months later, Android 18 later appears in the city with her family, until Android 17 attacks. 17 attempts to control her. However, Krillin intervenes, pointing out that Android 18 is now married and has a child. He also reminds Android 17 that he killed Dr. Gero himself, but 17's Machine Mutant counterpart, Hell Fighter 17, contacts him and regains control, causing him to kill Krillin. Krillin's death brings Android 18 back to reality, causing her to go in a rage and attack her own brother. Seeing what he has done, Android 17 then targets Marron so he can gain full control of Android 18, but Android 18 defends her from Android 17's energy wave, leaving her in a critical condition. Android 17 flies off to merge with Hell Fighter 17, and Android 18 crawls over to Krillin, taking his hand as she appears to die with him.
Later, Android 18 reappears and in an attempt to avenge her husband's death, she joins Goku in the struggle against Super 17. Through her intervention, she unknowingly reveals Krillin's death to Goku and she claims to have a bomb in her chest, though is bluffing as it was removed following the Cell Games. Her goading of Super 17 prevents him from finishing off her and Goku as he planned, leading to the super-android's self-emancipation by force from Dr. Myuu, who he kills with the blast that he intended for the pair and eventually his death when Goku finishes him off, Android 18 afterward proclaiming to have gotten vengeance for her deceased husband. It is at this point where Goku and Android 18 finally put their differences aside, the two having a talk after Super 17's death and Goku assuring Android 18 that Krillin would be resurrected, Android 18 accepting Goku as a true friend and ally.
Shadow Dragon Saga
Soon after the threat of the Shadow Dragons, Android 18 is seen at Capsule Corporation accompanied by Bulma, Chi-Chi, Videl, and Marron (her daughter).There is some debate as to whether or not Android 18 and her brother are still alive 100 years after the events of Dragon Ball GT (particularly during the time of the 64th World Martial Arts Tournament and the events of the special Dragon Ball GT: A Hero's Legacy). While Dr. Gero states that the process of reconfiguring the siblings into cyborgs has made the two immortal, this is contradicted by the special A Hero's Legacy, where it is narrated that Pan is the only character remaining from the generation of the original Z Fighters.
- Accel Dance – Android 18 and her twin Android 17 double team with a combo of punches and kicks, ending with their Power Falling Star technique.
- Afterimage Technique - A common technique used by many fighters. Used by 18 in Dragon Ball: Xenoverse.
- Android Barrier – A technique where energy is thrust out from the body in the form of a barrier with great force. The barrier can be used to both defend against oncoming projectiles as well as to expand and damage its surroundings, although only the former appears in Dragon Ball Z.
- Destructo Disc – A powerful razor-sharp disk of ki capable of slicing through nearly any opponent. This is the signature technique of her husband Krillin, who more than likely taught it to her.
- Dual Destructo-Disc – A team attack used by Krillin and Android 18 in the Nintendo DS gameDragon Ball Z: Supersonic Warriors 2.
- Double Destructo Disc - Android 18's variation of the Destructo Disc where she fires two Destructo Disc at the opponent in the form of a pincer attack, making the technique harder to avoid than her husband's standard Destructo Disc. 18's Ultimate Skill in Dragon Ball: Xenoverse.
- Energy Attack – The most basic form of energy wave used by androids.
- Energy Mine – Android 18's ultimate attack in Supersonic Warriors 2. She fires several concentrated, yellow spheres of energy around her opponent, which result in an explosion inflicting heavy damage.
- Finger Beam – A barrage of narrow rays emitted from the index finger of its user. Future Android 18 and her brother use this in The History of Trunks.
- Flight – The ability to fly without the use of ki.
- High-Pressure Energy Wave – A yellow Full Power Energy Wave fired from the palm of her hand. It gets its name from the Raging Blast games. It is called Energy Blast in Dragon Ball Z: Supersonic Warriors.
- Super Energy Blast – A powerful energy wave used by Android 18 in Supersonic Warriors.
- Non-stop Violence – Android 18 and Android 17, back to back, fire the Power Blitz and Photon Flashsimultaneously.
- Power Blitz – A strong energy wave fired from the palm of her hand. It is called Photon Blitz inSupersonic Warriors 2 and Power Beam in the Dragon Ball Z Collectible Card Game. In Dragon Ball: Xenoverse, she fires 2 strong energy blasts in the form of a pincer attack.
- Infinity Bullet – A rapid barrage of energy waves. Called Double Busterin Supersonic Warriors 2. In Dragon Ball: Xenoverse, it is called Endless Shoot.
- Photon Rain - 18's Final Ultimate Combo in Dragon Ball Z: Extreme Butōden.
- Quick Blast – A Continuous Energy Bullet attack used to hold off Semi-Perfect Cell when he is approaching to absorb her. She charges them similar to her Infinity Bullet attack, but fires a smaller amount of Ki Blasts.
- Power Falling Star – The technique used to finish the Accel Dance. Named in the Butōden series andBudokai series. It is called Photon Strike in Supersonic Warriors 2, and Full Power Energy Blast Volleyin the first Dragon Ball Z: Budokai Tenkaichi.
- 2x Photon Buster - 18's Ground Ultimate Combo in Dragon Ball Z: Extreme Butōden.
- Back Dash - Android 18's signature attack in the Raging Blast Series.
- Sadistic 18 – A rush attack used by Android 18 in the Budokai Tenkaichi series and Raging Blast series.
- Arm Breaker – The signature leg kick she uses to break her opponent's arm. She uses this against Vegeta, and later against Android 17. Named in the Dragon Ball Z Collectible Card Game.
- Buster Swing – The grapple toss that Android 18 uses during her Sadistic 18 attack. Named and used in the Budokai series.
- Deadly Dance – A rush attack where Android 18 generates a blue sphere on both hands, and then attacks the opponent with punches and kicks that knocks them into the air. Named and used in theBudokai series. In Dragon Ball: Xenoverse, the technique unleashes a series of dance-like kicks capable of deflecting ki blasts.
- Slap Attack – Android 18 swings her arm out attempting to hit the opponent with the back of her hand and if she connects, she goes into a slapping frenzy and finally slaps them away. It appears in theButōden series, as well as in numerous other video games as her grapple throw.
- So That's How it Has to Be! – The rush attack Android 18 used against Vegeta during their battle on theMountain Road. Named in the Raging Blast series.
- Hell Spiral – A team attack used by Android 18, Android 17, and Android 16 in Supersonic Warriors 2.
- Triangular Kick – She comes back a bit, then hops up-forward, and comes down-right at a 45 degree angle with a kick. Used in Butōden series.
- Flying Hip Attack – 18 jumps in the air and then comes down at a 45-degree angle, hitting her opponent with her hip. Used in Dragon Ball Z: Super Butōden 3.
- Flying Head Grab – A flying headbutt used in the Butōden series.
- Graceful Revolution – A low spin kick used in the Butōden series.
- Graceful Orbit – Turn around kicks used in the Butōden series. Android 18 performs a crescent kick, followed by a low spin kick.
- Energy Jet – A ground shave energy blade used in the Butōden series. Android 18 throws this ki blast down at the ground, and it travels along to ground towards the enemy.
- Flash Beam – An explosive energy sphere Androids 18 throws on the ground to attack her opponent. One of her super attacks in the Butōden series.
- Meteo Bloody Drive – Android 18's meteor attack in Dragon Ball Z: Ultimate Battle 22.
- Power Strike – Android 18 kicks the opponent up in the air, and then she kicks and punches them down again. Used in the Budokai series.
- Destructo Missiles – Android 18 fires three missile out of her back, and they home in on the opponent, causing major damage. Used in Dragon Ball Z: Taiketsu.
- Violence Hold – One of 18's techniques in Super Dragon Ball Z. Also used by 17.
- Savage Combo – A powerful kick combo used in Super Dragon Ball Z. Also used by 17.
- Infinity Hold – Android 18 charges at the enemy, attacks them, then flips them down into the ground. Used in Super Dragon Ball Z.
- Power Regen Kiss (気力回復キッス) – Android 18 blows a kiss which stuns her opponent. Used in the arcade game Dragon Ball: Zenkai Battle Royale.
- In Shin Budokai, Android 18 reveals that she is capable of detecting other Androids, as she does so when trying to get back up against Broly, though she is unsuccessful in locating any nearby. She also reveals that she can detect the waves emitted by Dragon Balls.
- Energy Absorption - In Dragon Ball: Xenoverse, 18 is capable of absorbing an opponent's ki and stamina depending on the Energy Absorption Super Skill being used.
- Drain Charge - 18's ki absorption skill.
- Super Drain - 18's Stamina absorption skill.
- Hyper Drain - 18's ki and Stamina absorption skill.
- Super Electric Strike - An Ultimate Skill used by her brother Android 17and non-playable versions of her in Dragon Ball: Xenoverse.
- Rolling Bullet - One of 18's Evasive Skills in Dragon Ball: Xenoverse.
- Meteor Crash - One of the Meteor Attacks which 18 can use in Dragon Ball: Xenoverse.