When the Red Skull sought an heir for his criminal empire, he fathered Sinthea Schmidt. The girl was raised with constant indoctrination of her father's twisted views. Forced to undergo physical transformation in one of the Red Skull's machines, she was gifted with superhuman powers. With her partner Crossbones and an incarnation of the Serpent Squad by her side, Sin has rampaged across the world, coming into conflict with the Avengers, S.H.I.E.L.D., and the Winter Soldier.