The Avengers: Hulk
Marvel had a lot of characters and a lot of good characters, with Bruce Banner (The Hulk) being quite possibly one of the best. He is in fact one of Marvel's fan favorites due to his tragic story of being a man with tremendous power but constantly being afraid of it. With the burden of his powers he would frequently be found in his own solitude until he was able to control the beast inside of him. With his love interest, Betty Ross, you could compare the story of The Hulk to that of Disney's Beauty and the Beast. Betty, despite his dark side, saw him for who he really was. She saw him as man with a big heart while her military man father saw him as an enemy of the state and treated him as such. His inner struggle also helped to make him one of very few comic book characters that people could easily identify with. His powers came from the gamma radiation that he worked with which turned him into the Hulk. As the Hulk, he is a force to be reckoned with. His strength, speed, and durability are greatly increased on top of his accelerated healing factor.
Bruce Banner was the son of an atomic physicist Brian Banner, and his wife Rebecca. Brian was an alcoholic and hated his son due to the amount Rebecca loved her child. He never felt that his love for Rebecca was reciprocated and became increasingly more jealous of Bruce. Furthermore, Brian believed that his work with radiation had altered his DNA giving him a mutant son. With all of this in mind, Brian eventually snapped in a fit of rage where he abused Bruce and eventually killed Rebecca which quickly placed him in a mental institution. Bruce became a highly withdrawn child but incredibly smart making him a pseudo child prodigy. He would then be raised by his aunt but as a child he repressed all of his past misfortunes which drove him to his own solitude. As he grew up he became smarter and studied nuclear physics eventually getting a doctorate in the field. In his adult years where he was a genius in the field of nuclear physics, would go on to work for a United States Defense Department nuclear facility in Desert Base, New Mexico. There he would meet Thaddeus "Thunderbolt" Ross, the Air Force officer in command of the base and his daughter Betty who he would fall in love with. Thunderbolt Ross never truly thought Bruce was entirely right for his daughter, and after horrible events, he did everything in his power to see to it that Betty would never be with him. Banner oversaw construction of the "Gamma Bomb" a nuclear weapon possessing a high gamma radiation output. Banner was present at the test site of the first underground test of the bomb and observed that a civilian had breached security entering the restricted area. He told his colleague to delay the countdown so he could get the civilian to safety, but his colleague was in fact a Soviet spy hoping to see Banner killed in the blast. Before Banner could to safety after putting the civilians life first, it detonated with him in danger while also intense waves of radiation reached the surface. Banner was irradiated with highly charged radioactive particles. Most likely from his father's previous work with radiation affecting his DNA, Banner was not killed in the explosion. Instead, the accident caused him to turn into the vastly powerful, grey-skinned humanoid monster named "the Hulk."
Banner's body eventually changed so that his transformations into Hulk were triggered the release of adrenalin which coincided with him becoming increasingly angry or any kind of emotion. The Hulk also rarely retained any memory or intelligence and was easily enraged. Equally so when he was in the human form of Bruce Banner, he would often just get glimpses of what he has done as the Hulk. For instance, say he was being shot as the Hulk, Bruce would hear something similar to a gun shot and get scared. A sort of visual memory if you will. Due to what happened in the defense facility, the military tried to contain the Hulk as they viewed him as their own personal property and a danger to everyone else. However, every one of their attempts were thwarted. Banner maintained his identity as the Hulk a secret while attempting to keep it a secret. Banner's next transformation into the Hulk had his skin color change green, which happened to be his his most constant skin tone. In an effort to control his transformations, Banner created a Gamma Ray Projector to force transformations into the Hulk and then back into Banner. It worked in theory, but his Hulk persona was reluctant to transform back into Banner. The Hulk was eventually shot out into space where he passed through a radiation storm which then allowed Rick Jones to control him. Upon his return, he and Rick Jones, who was the civilian that he saved from the Gamma radiation, worked together to stop the Circus of Crime, after the two disposed of the villains, Jones no longer had control over the Hulk.
Loki, the trickster brother of Thor, used the Hulk as a pawn by tricking him into fighting Thor. This plot went horribly wrong for Loki as the Hulk joined forces with Thor, Ant-Man, Wasp and Iron Man to form the Avengers and defeat Loki. This was their first real act as a team and brought them together rather quickly. As a team they even clashed with the Fantastic Four's super villain Victor Von Doom, also known as Doctor Doom. The group however never fully trusted the Hulk as he was somewhat a wildcard due to his uncontrollable and erratic behavior. After the teams run in with Space Phantom where he feasted on the team's mistrust, it forced the Hulk to quit. He became shortly after a more permanent fixture of the Avengers lineup despite his erratic behavior.