Bruce Banner, whose alter-ego is the Hulk, a monstrous beast created by an accidental overdose of Gamma radiation, is searching for a cure for his affliction while being chased by General Ross and the government bent on the Hulk's destruction.

Clint Barton a.k.a Hawkeye was an agent of SHIELD until the betrayal of Black Widow.

Biophysicist and nanotechnology expert Dr. Henry "Hank" Pym a.k.a Ant Man discovered a size altering chemical that allowed him to alter his size from a giant to the size of an ant.

When Bruce Banner becomes angry, the accidental overdose of Gamma radiation he received transforms him into the Hulk, the almost mindless force of nature relentlessly pursued by General Ross and the government.

Janet Van Dyne a.k.a The Wasp has the ability, thanks to the implantation of sub-atomic Pym particles, to shrink down to insect size and fire laser blasts from her hands.

Nick Fury is the head of SHIELD (Strategic, Hazard Intervention, Espionage Logistics Directorate)

Thanks to an experimental serum developed to create a WWII super soldier, Steve Rogers became Captain America. He quickly championed the cause against HYDRA and it's leader The Red Skull.

After witnessing his fathers death in a ritual leadership contest, T'Challa took up the mantle of Black Panther to free his people from the tyrannical rule of Man Ape.

Thor is the hammer wielding god of thunder. He has come to Midgard (Earth) against his father Odin's wishes to assist in the protection of the human race.

Billionaire Tony Stark, founder and head of Stark Industries, created the Iron Man suit after suffering a heart injury when he was kidnapped and forced to create weapons. Instead he created the suit and now helps defend the world against aggressors.