Gamora
Gamora is the last of her species, the Zen Whoberi, who were exterminated by the Badoon. Thanos found the child and decided to use her as a weapon. Gamora was raised in an alternate time, and trained by Thanos to assassinate the Magus, and Thanos showed her little kindness during her childhood, but Gamora was very loyal to the man who promised her the opportunity to avenge the death of her family.
Gamora was sent as an assassin against the Universal Church of the Truth, and she exacted revenge for the genocide of her race by killing every member of the church involved before the event actually occurred. Gamora met and teamed up with Adam Warlock, but failed her assassination in the last second. Eventually the Magus was defeated, but Thanos revealed himself as an even greater threat. Gamora tried to prevent Thanos from destroying all life in the universe, but he mortally wounded her and her sould was absorbed into the Soul Gem of Adam Warlock. It was later released, and she returned to existence.