Jennifer Walters is the cousin of Bruce Banner, the Hulk. After an attempt on her life left her in critical condition, a blood transfusion from Banner infused her with gamma irradiation and transformed her into the savage and sensational She-Hulk.
While she gained much of the superhuman strength of the Hulk, Walters retains her sharp wit and honed sense of justice when she transforms, becoming a less inhibited version of herself. She rarely sees the need to return to her original self, preferring instead to fight crime with her immense strength and durability.