Vandal Savage was an immortal who lusted for power.
25,000 years ago, his prehistoric tribe witnessed an asteroid fall to earth. While his fellow men ran away from it in fear, the man then known as Vandar Adg walked up to it and slept by it, as the night was cold and it provided warmth. Where the rock came from was never known, but its radiation and heat transformed him for life. Only a couple decades later did he realize he would never age — while his brothers, sisters and tribesmen passed on and on, Savage continued in his present form — never changing physically, but always evolving mentally
The Justice League first encountered Vandal Savage when they returned to Earth and found it altered as a result of his tampering with history. Having invented a time machine, Savage sent a "gift" to his younger self during the era of World War II: a laptop computer containing schematics for advanced technology, and knowledge of the future that would help him overcome the Allies. Using this information, Savage supplantedAdolf Hitler, placing him in suspended animation, and took control of the Nazi German regime. With his highly advanced technology, as well as knowledge of future events such as D-Day, the Axis Powers easily defeated the Allies. As a result, Vandal Savage became the undisputed dictator of the world.
However, the League traveled back in time through Savage's time portal and prevented Savage's plans from happening, managing to destroy the laptop. They also thwarted his attempted airborne invasion of the United States, and they assumed Savage was killed when one of his planes crashed into the Atlantic Ocean. In order to cope with Savage's failure and the loss of their leader, the Nazis reinstalled Hitler, and thus the war ended as an Allied victory. Due to the League's actions, Savage's reign was stopped in its infancy.
Savage showed up again to face the Justice League in the early 21st century, initially posing as his own grandson to conceal his immortality from public knowledge. As the head of Kaznia's space program, he oversaw its substantial contribution to an International Space Station, and became sufficiently well-regarded by the King, Gustav, to become affianced to Princess Audrey, the heir to the throne. After poisoning Gustav with the help of a treacherous maid, Savage induced Audrey, his trusting fiancée, to take up her father's crown and rule Kaznia. This allowed Savage to reveal his plan to the world: an orbital rail gun mounted on the space station allowed him to fire asteroids at earth with pinpoint accuracy and devastating effect.
Luckily, Green Lantern, Flash and J'onn J'onzz boarded the station in time to set it to self-destruct — but not before a final asteroid was fired. On Earth, Batman and Wonder Woman freed Audrey from Savage's clutches, and Batman managed to change the asteroid's target to Savage's own headquarters. Civilians escaped, while Savage was buried under the rubble — but, like the immortal being he was, he rose up again, popped his bones back into place and lived on. Audrey had him arrested on the spot, promising he would pay for his crimes. Savage sneered that no one could kill him and invited her to do her worst, and Audrey intended to do just that.
Savage was immortal, meaning he did not age and had healing abilities that allowed him to survive any injury that would maim or kill a normal human being.
Being a prehistoric man, he was already exceptionally strong before his transformation, and continued to grow in strength to a nearly superhuman level.
His long life gave him vast knowledge, a genius-level intellect, and great technological inventiveness, which includes the invention of the time machine.
Finally, because Savage had literally "all the time in the world," his plans, when sprung, were always well-prepared in advance and difficult to upset.