The Shinobi is a minor antagonist in the show who is actually a robot.
Shinobi was one of the many subordinates that Aku sent to kill Jack. He was about Jack's height, wore a black ninja outfit called a Shinobi Shizoku, had a black sword he wore on his back, and had red eyes. He was a master of stealth and assassination and practiced against Samurai Jack droids to perfect his art.
Shinobi first appeared in what seemed to be some sort of temple where Jack was praying, swiftly and without sound approached the Samurai and quickly cut him down before the latter could reach for his blade. However this was revealed to be a simulation in order for Aku to test the bounty hunter's skills. Satisfied, he sent Shinobi to kill Jack. He is later seen stalking Jack in a jungle, but before he could attack, a small boy ran out of some bushes while a robotic lobster-like creature was chasing him. After seeing this, Shinobi hid in the shadows and continued to follow Jack. After the latter defeated the robot, Shinobi kidnapped the young boy seen earlier and took him to an abandoned tower as bait. Jack soon arrived at the tower and was attacked by Shinobi, but managed to save the boy. After the boy went to safety, Jack decided to fight Shinobi at his own game, but used the light instead of the darkness to hide. The two were evenly matched, but with the sun setting, Jack was slowly lose his hiding spots. In the end, Jack defeated Shinobi by reflecting the last sliver of light into it's eyes, blinding him and causing him to drop his guard. Jack finished Shinobi by throwing his sword at him, impaling him to a post and cutting him in half.
- Master Infiltrator: Shinobi could infiltrate any area or building without being detected, even by Jack.
- Martial Arts Master: Though he specialized in assassination, Shinobi was highly proficient in hand-to-hand combat, utilizing punches and kicks with his sword, catching his opponents off guard.
- Master Swordsman: His skill was great enough that, when neither he nor Jack had the use of their particular element, he held a slight but noteworthy advantage against Jack in open combat.
- Master Camouflage: Shinobi can become completely invisible and undetected whenever in any shade of darkness.
Shinobi's Ninjato: Shinobi wield's a black sword as his main weapon and tool to carry out assassinations.
- Episode XL: Samurai versus Ninja