Gamora

She was a member of a pacifistic race called the Zen Whoberis. They were slaughtered by the Badoon, a warlike alien race. In the midst of the bloodshed, Thanos teleported in and saved Gamora. She was the only survivor of the mayhem.

Thanos quickly went about turning Gamora into a living weapon. He trained her in all the fighting techniques he could. Although she was very deadly, she ran afoul of a street gang at a spaceport. They raped her and beat her. As a result of the brutal treatment, she had most of her bones replaced with a lightweight metal alloy, and her strength and reflexes enhanced.

She died in Avengers Annual #7, killed by Thanos when she questioned his plans to destroy the universe. Adam Warlock kept her soul alive in his soul gem. When she was brought back to life in a new form, her abilities were once again increased. She guarded the time gem as a member of The Infinity Watch. This got her into all sorts of cosmic plots, and she even had a semi-important role in The Infinity War. However, she quit The Infinity Watch, and her time gem was given to Maxam. Since the events of Thanos: Infinity Abyss, she has been watching over the anchor of our reality with Adam Warlock, and the two are enjoying a sweet little relationship.