Hulk

: "I spent a lifetime running from this aspect of myself. Denying half of your being is no way to live, trust me."
: ―Bruce Banner to Jennifer Walters[src]
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 tasked 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 substituted vita radiation for gamma radiation and administered the serum on himself. 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.
For five years, Banner remained on the run from the United States Army. He chose to live a discreet life in South America while 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, but was captured shortly thereafter at Grayburn College. Blonsky, who had received a variant of the Super Soldier Serum, was administered Banner's gamma-irradiated blood, transforming him into Abomination. This new threat forced Ross to allow Banner to turn into Hulk and battle Blonsky, before allowing Banner to escape.
After a failed suicide attempt, Banner focused on helping people. However, when Loki attacked S.H.I.E.L.D., Banner was personally recruited by Natasha Romanoff to aid Tony Stark in tracking down the Tesseract. Despite losing control and attacking the Avengers on the Helicarrier, Banner joined the Avengers during the Battle of New York, assisting them in defeating Loki and the Chitauri, ending their invasion.
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 Baron Strucker. With the Scepter in their custody, Banner assisted Stark with creating Ultron, an artificial intelligence peacekeeping program. Ultron, programmed to protect Earth at all costs, deemed humanity and the Avengers as the world's greatest threat and focused on annihilating them. Banner and Stark created Vision as a deterrent to Ultron, and participated in the Battle of Sokovia to dismantle Ultron's threat. After Ultron's defeat, Hulk commandeered a Quinjet and left Earth.
During his interstellar travel, Banner came across a wormhole that caused him to crash on Sakaar. There, the stressful environment prevented him from returning to his human form, causing him to remain in Hulk form. For two years, Hulk's consciousness grew as he 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, Hulk fought against his old friend in the arena. In the wake of their fight, Thor informed Hulk that Asgard was under threat due to Hela's return. Despite Hulk's protest, Banner managed to retake control of the body, agreeing to help Thor in his plight. While witnessing the Asgardians in peril, Banner transformed back into Hulk and aided the Asgardians in their fight, defeating Fenris and allowing the Asgardians to board the Statesman. Hulk witnessed as Ragnarök was fulfilled and Asgard was destroyed, and elected to stay with the Asgardians as they decided to travel to Earth.
Months later, the Statesman was attacked by the Black Order, who massacred half of the passengers. Hulk fought their leader Thanos, who quickly defeated him before Heimdall used the Bifrost Bridge to transport him to the New York Sanctum. Shifting back to Banner, he warned Doctor Strange, Iron Man and later Captain America of Thanos' upcoming arrival. With Hulk unwilling to transform, 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 completed the Infinity Gauntlet, wiping out half of the universe's population. Having survived the Snap, Banner joined the Avengers on their trip to the Garden, where Thanos was killed.
After the Snap, Banner went to Mexico and worked with Stark to merge his consciousness with Hulk's body to become Smart Hulk, after which he became an adored celebrity. In 2023, he rejoined the Avengers to help them use Pym Particles and the Quantum Realm to travel through time to alternate universes. After traveling back to the Battle of New York in an alternate 2012, Banner successfully acquired the Time Stone and returned to the present. Using the Nano Gauntlet, Banner used the Stones to initiate the Blip, resurrecting all the lives claimed by the Snap, albeit injuring his right arm in the process. After participating in the Battle of Earth, he attended Stark's funeral before he sent Captain America back in time to return the stones to their respective universes.
By 2024, Banner had constructed the Hulk Inhibitor Device to return to human form so that his arm could heal. Along with Captain Marvel, Banner was called upon by Wong to aid in investigating the mystical Ten Rings which Shang-Chi had harnessed. After his cousin Jennifer Walters came into contact with his blood and gained the ability to transform into She-Hulk, Banner advised her on how to deal with her new abilities before leaving Earth on a Sakaaran ship. He later returned to Earth in order to introduce his family to his newly discovered son, Skaar.