While lightning may never strike the same place twice, the same can't be said about gamma radiation and relatives of the Bruce Banner clan. Although the long suffering Hulk paid the price for saving his future sidekick/best friend Rick Jones from that famous gamma radiation experiment in the desert, that very same heroism would one day change the life of his cousin Jennifer Walters. Due to Bruce's intervention, Jennifer Walters would also go by another name, the Sensational She-Hulk -- with a similar power set and, thankfully, a more fashionable wardrobe.
In Savage She-Hulk #1 (1980) written by Stan Lee and drawn by artists John Buscema and Chic Stone, the ever-paranoid and wandering Bruce Banner is evading the authorities and people looking for him but can't resist going to L.A. to see his cousin Jennifer Walters. The two relatives reunite and catch up as Bruce tells Jennifer the story of how he became the Hulk and why he must always be on the run, confessing to someone who was more like a sister than a cousin to him. During their reunion, Jennifer tells him about her latest case against a local crime boss and how she planted a false rumor to draw him out. The criminal, Nick Trask, responds with two hired guns who shoot Jen and would have killed her... if not for the timely intervention of her cousin Bruce.
Recognizing the empty house of a neighborhood doctor, Bruce breaks in and attempts to save his dying cousin with an emergency blood transfusion. While Bruce stays behind and evades the police's questioning, he only leaves L.A. once he learns that Jennifer will make a full recovery, reasoning that she'll be safer without him.
While Jennifer recovers and tries to understand Bruce's absence, Trask's hitmen return disguised as doctors to finish the job. As she is restrained, her anger gets the best of her and before her would-be killer's eyes, Jen transforms into a taller, green-skinned version of herself complete with super strength and super anger issues. Enjoying the observation that one of the assassins made about her appearance, the newly-dubbed She-Hulk stops their second murder attempt and they quickly flee the room.
Unwilling to let them escape justice, She-Hulk pursues them in and outside the hospital showcasing her new strength until she gets a confession. Leaving her new witnesses with the arriving police, She-Hulk flees the scene with enough time to transform back into timid Jennifer Walters and conveniently sneak back into the hospital before anybody notices she's been gone. This simple pattern is the kind of Marvel stories that Stan Lee was known for, but the simplicity lays down basic groundwork for others to continue right where this impressive creative team left off.
Since then, Jennifer has continued to be a lawyer and have multiple adventures alongside her (in)famous cousin, other Marvel superheroes and is currently a member of the Avengers. With solo series in development on Disney+, now might be a time to acquaint yourself with the other green-skinned powerhouse in the Marvel universe. On another unrelated note, Marvel superheroes have since then exercised extreme caution in donating blood.