Hulk

The Hulk is a 9 foot tall creature that is the form of Bruce Banner when angered or stressed. This is due to exposure to gamma radiation during an experiment attempting to find a way of making humans immune to gamma radiation.

The Incredible Hulk
A series of flashback shots show the gamma radiation accident that transformed scientist Bruce Banner into the Hulk, and hospitalized his lover Betty Ross. Now a fugitive from the United States Army, and Betty's father, General Thaddeus Ross, Banner goes on the run for five years. He settles in Brazil, working in a soft drink bottling factory while attempting to find a cure for his condition with the help of an Internet friend, "Mr. Blue". He also studies martial arts and meditative breathing techniques with a Brazilian Jujitsu expert to help control his emotions, and has not suffered a transformation for five months.

After Banner suffers a cut, and his blood drips into a soda bottle eventually drank by an ill-fated consumer in Milwaukee, Wisconsin, Ross discovers Banner's location, and sends a team to capture him, led by Russian-born British special operations expert Emil Blonsky. Following a ferocious battle in the soft drink bottling plant where he transforms into the Hulk, Banner escapes Blonsky, and ends up in Guatemala. He travels to the United States, where he sees that a now-recovered Betty is working at Culver University and is dating psychiatrist Leonard Samson. He also sees his old friend Stanley, a pizzeria owner, who gives him a job as a delivery boy. Banner uses this job to sneak past a security guard to continue his research. After Betty visits the pizzeria and sees Bruce, she later reunites with him.

Blonsky reports to Ross that Banner evaded them in Brazil because of the appearance of a large green monster. Ross explains that the monster is Banner, and that he was created accidentally during an experiment in radiation-resistance that was inspired by World War II era military bio-force enhancement research (or "Super-Soldiers", as Blonsky puts it). Blonsky, seeking both revenge and power, volunteers as a test subject in order to capture Banner. He receives a small dose of the mothballed original Vita Ray serum, created by Dr. Reinstein for Weapon Plus. He leads an assault on Banner at Culver University, during which Betty is knocked unconscious. Despite Blonsky's increased strength, speed and agility, the Hulk crushes most of the bones in Blonsky's body. The Hulk saves Betty from an explosion and escapes with her to the Smoky Mountain National Forest.

Banner and Betty then travel to Empire State University in New York City, where they meet "Mr. Blue", Samuel Sterns. Accompanying Sterns to his lab, Banner and Betty learn that Sterns has developed a possible antidote that may cure Banner's condition or merely reverse each individual transformation while an overdose could kill him. Despite the risks, Banner agrees to test Sterns' antidote and is restrained before being shocked into transforming with electricity before being reverted to normal with an injection of the serum. Exhilarated by the success of the antidote, Sterns reveals that he has synthesized Banner's blood sample into a large supply with the intention of using it to enhance the human condition to the next evolutionary level. Appalled by what Sterns had done and fearful of the Hulk's power falling into the wrong hands, Banner attempts to convince Sterns to destroy the blood supply but is shot by a tranquillizer from one of General Ross' snipers.

As both Banner and Betty are taken into custody, Blonsky, whose super-soldier treatment has healed all his injuries but is desperate for more power, demands Sterns subject him to a dose of the Banner's gamma radiation treatment. Sterns warns that the combination of the Super Soldier formula and a gamma treatment would be an unpredictable combination that could turn him into an "Abomination". Blonsky is less than concerned about this, and Sterns promptly administers the gamma charge. As Blonsky mutates into the monstrous Abomination, he knocks Sterns aside and an irradiated sample of Banner's blood-derivative drips into an open wound on Sterns's temple, causing his cranium to mutate and expand. In an attempt to draw the Hulk out, the Abomination goes on a rampage through Harlem and Banner, realizing that he is the only one who can stop the Abomination, convinces General Ross to release him. He jumps out of Ross' helicopter as it hovers over the city, hoping the fall will stimulate his adrenal glands into triggering a transformation. Banner's plan succeeds and after a brutal battle the Hulk manages to defeat the Abomination by strangling him with a huge chain, though he releases his grip after a plea from Betty. The Abomination collapses, and the Hulk flees the scene with the army in hot pursuit.

Thirty-one days later, Banner is in Bella Coola, British Columbia. Instead of trying to suppress his transformations, he is attempting to initiate them in a controlled manner. As his eyes turn green, a grin appears on his face.

Iron Man 2
When Nick Fury debriefs Tony the screen on the right shows the report of the attack on Culver University which was in fact the Hulk.

Thor
Erik Selvig mentioned Banner as the pioneer in gamma radiation. Then S.H.I.E.L.D came and he wasn't heard from since.

The Avengers
Banner is working as a doctor in India having not transformed for over a year. He is tricked into contact with Natasha Romanoff by a little girl and is brought into the Avengers Initiative. After meeting members of the team on the S.H.I.E.L.D helicarrier, Banner and Tony Stark begin research on the recently captured Loki's spear. When the team begins to spark unnessessary arguments, the brainwashed Hawkeye leads a team into the ship and explodes one of the engines, causing Banner and Romanoff to fall into the weapons cache room. Banner transforms unwillingly despite Romanoff's efforts to calm him down and ends up falling off the helicarrier after causing much destruction and even throwing down with Thor. He eventually transforms back to Banner to find himself having been watched falling by a man. The man gives Banner new clothes.

Banner returns to fight in the war in New York and finally reveals his secret of keeping calm: he is always angry. Banner transforms into Hulk and takes out a Leviathan with one punch then aids the Avengers in the battle. After assisting Thor, Hulk enters the Stark Tower and beats Loki into submission. The World Security Concil eventually send a missile to destroy Manhattan. Stark flies the missile to the Chitauri's portal, though his suit shuts down in the progress. Hulk catches Stark and screams in his face, waking him up. After Loki is sent back to Asgard with Thor and the Tesserect, Banner and Stark drive away in one of Stark's sports cars and then the team go their separate ways.

Abilities
The Hulk is one of the most powerful beings on the planet since his powers increase with his rage. He is capable of matching the strength of beings like Thor and the Abomination.
 * Superhuman Strength: The Hulk´s primary power is his superhuman strength, enabling him to do feats like split a car in two with just two punches, he stopped an Humvee in its track and picked it up and slammed into a tree a couple of times, he also took the entire engine of the same Humvee and threw it into another Humvee, making it explode, throw Emil Blonsky more than 40 feet away with just one kick, even though the latter has been given great resistence, and throwing a forklift truck in the air very easily. He can throw normal humans around like ragdolls. In the form of the Hulk, Bruce possesses immense physical strength. As the Hulk he was able to rip steel as it was made of paper and was able to throw heavy objects with tremendous force. He is also capable of leaping great distances. By clapping his hands he was able to make a shockwave that snuffed out a fire. His strength is only rivalled by the Abomination or Thor. In times of stress the Hulk's adrenaline level escalates, causing a corresponding escalation in strength. This is not accompanied by an additional gain in mass, but does appear to promote increased levels of energy efficiency. To date the Hulk has never apparently been provoked into demonstrating a maximum output of strength, hence his upper limit remains a mystery. However, whatever the limit, it is well in excess of 100 tons. This is also displayed when seeing Betty in danger in the damaged helicopter, he outmuscled the Abomination to free himself. By raising his fists and arms and striking the ground (accompany by one of his classic lines "Hulk Smash"), he can create tremors of incredible force that stun the Abominaiton. In his fight with Thor he was able to hit him hard enough to make the thunder god bleed.
 * Weaponization: The Hulk demonstrates the ability of using his strength to turning anything in the envirnoment around him into weapons and/or armor to use. During the battle at Culver University, he turn pieces of a Humvee into a shield to use when Blonsky attacked him with a grenade launcher, using one piece to protect him against the waves of the sonic cannons and using the same piece to destroy one of the Humvees carrying one of the sonic by throwing it and splitting in half and then talking the other piece to jump into the other Humvee and basically jump diving into it and using it to destroy an attacking Apace helicopter. Finally, during the battle with the Abomination, he split a cop car in half and use it as boxing gloves to beat into Blonsky and using a large chain that Blonsky was using to nearly choke him to death before being stopped by Betty.
 * Superhuman Durability: The Hulk has incredibly tough skin, allowing it to easily withstand bullets which don't even pierce its skin. He can even withstand weapons made from the Tesseract with little difficulty. Only beings with tremendous force or extremely powerful weapons can harm him.
 * Superhuman Endurance: Substantially greater endurance than a normal human.
 * Superhuman Speed: The Hulk is capable of running faster than a human; he was able to keep up with Blonsky.
 * Superhuman Leaps: Hulk has been shown to be able to make mile-sized leaps that can be incredibly precise in landing.
 * Instantaneous Regeneration: The Hulk displays an incredibly fast rate of regeneration. This grants immunity to any illness and longevity (for Hulk, not Bruce). The Hulk heals rapidly from injuries at a much greater rate than a normal human.
 * Martial Artist: The Hulk, while having no formal training, is a formidable hand to hand combatant simply due to his great physical attributes. He typically uses street fighting and brawling techniques that make full use of his strength.

Relationships

 * Betty Ross - Lover
 * Captain America - Avengers teammate and team leader
 * Iron Man - Avengers teammate
 * Thor Odinson - Avengers teammate
 * Black Widow - Avengers teammate
 * Hawkeye - Avengers teammate
 * Nick Fury - Ally
 * Erik Selvig - Ally
 * Loki Laufeyson - Enemy
 * Thaddeus Ross - Enemy
 * Abomination - Enemy
 * The Leader - Ally turned Enemy
 * Chitauri - Enemies

Trivia

 * There are several noticeable visual differences between The Hulk in The Incredible Hulk and The Avengers, despite the fact they are both in the same continuity. The Hulk in The Incredible Hulk is much taller and muscular then he is in The Avengers, and dark green skin, whereas in The Avengers he has brighter skin and a shorter hair cut. Their faces are also different. Much of these differences are because Mark Ruffalo is using motion-capture to actually play the Hulk, whereas Hulk was entirely CGI in The Incredible Hulk.