Hulk

"' In case you needed to kill me, but you can't. I know! I tried! I got low. I didn't see an end so I put a bullet in my mouth, and the other guy'- Bruce Banner"

Doctor Robert Bruce Banner, M.D., Ph.D., is a renowned scientist and a founding member of the Avengers. Highly respected for his work in biochemistry, nuclear physics, and gamma radiation, Banner was commissioned by Thaddeus Ross to recreate the Super Soldier Serum that created Captain America. However, Ross elected not to inform Banner what he was creating. During the experiment, Banner was exposed to dangerous levels of gamma radiation (rather than vita radiation). As a result, the mild-mannered scientist found that when angered, provoked, or excited, his body and brain would transform into a huge, rage-fueled, primitive-minded creature known as the Hulk.

Fearful of the damage that Hulk could inflict and wishing to flee from the United States government, Banner attempted to kill himself. When the attempt failed, he chose to live a discreet life in South America while also communicating with Samuel Sterns to cure himself. However, when General Ross sent a team led by Emil Blonsky to apprehend Banner, Banner was forced to return to New York City. He recruited the help of Betty Ross and Sterns to cure him of his affliction. Banner was apprehended by the Armed Forces shortly after. However, Blonsky, who had received a variant of the Super Soldier Serum, was administered Banner's gamma-irradiated blood, transforming him into the Abomination. This new threat forced Ross to allow Banner to turn into Hulk and battle Blonsky, before allowing Banner to escape.

Banner fled the United States and dedicated his time to aiding the sick and poor. When a mounting threat called for Banner's specialized scientific expertise, S.H.I.E.L.D. recruited him, knowing full well that the incredible strength of Banner's alter-ego would be an additional asset to the Avengers. Banner was tasked with tracking down the Tesseract, working alongside Tony Stark to achieve this. Despite almost causing a disaster when Loki's schemes caused Banner to transform into Hulk aboard the Helicarrier, Banner later joined the Avengers during the Battle of New York, assisting them in defeating Loki and his Chitauri army. Once the Avengers split up in the wake of the battle, Banner had become good friends with Stark and relocated to Avengers Tower, free to live his life without apprehension.

In the wake of the HYDRA Uprising, the Avengers regrouped once more to battle the ever-growing threat of HYDRA, successfully capturing Wolfgang von Strucker and retaking the Scepter. In order to make it so that Earth could always be safe without constantly needing the Avengers to protect it, Banner assisted Stark with creating Ultron, an artificial intelligence. Ultron, programmed to protect Earth at all costs, deemed humanity and the Avengers as peace's greatest threat and focused on annihilating them. Banner was then enlisted by Stark to help create Vision, and was later coaxed by Black Widow into transforming into Hulk and help defeat Ultron. Following Ultron's defeat, Banner commandeered a Quinjet and left Earth, flying into space and coming across a wormhole that caused the Quinjet to crash on the alien planet of Sakaar. There, the stressful environment prevented him from returning to his human form, causing him to remain in Hulk form for two years.

On Sakaar, Banner became a gladiator for Grandmaster and was soon revered as a beloved champion, choosing to turn his back on Earth and enjoy the life of an admired warrior. However, when Thor arrived on the planet, Banner fought against his old friend in the arena. In the wake of their fight, Thor informed Banner that Asgard was under threat due to Hela's return. Eventually, Banner returns to his human form, agreeing to help Thor in his plight. He transforms back into Hulk and aids the Asgardians in their fight, defeating Fenris and allowing the Asgardians to board the Statesman vessel. Then, as Ragnarök was unleashed, Banner joined them on their voyage to Earth.

On their way back to Earth, the Statesman was attacked by the Black Order, who killed half of the Asgardians. Banner challenged their leader, Thanos, who quickly defeated him. He was then teleported to the New York Sanctum by Heimdall, where Banner warned Doctor Strange, Iron Man, and later Captain America of Thanos' arrival. Finding himself no longer able to transform into Hulk, Banner operated a Hulkbuster armor to aid the Avengers in the Battle of Wakanda. Although Banner and his allies managed to kill off Thanos' forces, Thanos personally arrived in Wakanda to retrieve the Mind Stone. He effortlessly subdued Banner and the other heroes and completed the Infinity Gauntlet, wiping out half of the universe's population. Banner was one of the survivors.

At some point after the Snap, Banner permanently merged his consciousness and Hulk into one being, which combined Hulk's raw strength and physique with Banner's mind and intelligence, becoming an adored celebrity. In 2023, he rejoined the Avengers to help them use Pym Particles and the Quantum Realm to travel through time. After traveling back to the Battle of New York in 2012, Banner successfully gained the Time Stone from the Ancient One and returned to the present. He and Rocket Raccoon helped Tony Stark design the Nano Gauntlet to contain the Stones the Avengers had collected. Banner elected to use the Stones to resurrect all the lives claimed by the Snap, injuring himself in the process. In the aftermath of the Battle of Earth, which resulted in Iron Man's death, Banner sent Captain America back in time. Shortly after, he reverted to his human form, his right arm still in a sling; however, all the scarring had healed.