Gamora
Abilities: Gamora is a Zehoberei, an alien species that naturally possesses superhuman strength and durability. She was trained and cybernetically enhanced by Thanos, who called her "the fiercest woman in the galaxy." He regarded her more highly than any of his other "children" or soldiers.
Power scale: 6.5. Gamora is similar to Black Widow: She was raised, nearly from birth, to be a ruthless assassin and has proven her prowess many times over. But she has natural abilities that far surpass non-enhanced human beings, and she earned a fearsome reputation throughout the galaxy before turning on Thanos. As Rocket told her, "Anyone who's anyone knows who you are."