Marvel

Captain America - A scrawny fine arts student who grew up during the Great Depression, Steve Rogers was injected with the Super Solider Serum, giving him superhuman strength and agility.

First Appearance: Captain America Comics #1

Deadpool - The Merc with a Mouth... While he is incredibly silly, Deadpool is one of the most effective mercenaries out there.

First Appearance: The New Mutants #98

Doctor DOOM - Victor von Doom is a genius and ruler of Latveria. Often thwarted by the Fantastic Four, he uses his incredible mind and vast resources in repeated attempts at world domination.

First Appearance: The Fantastic Four #5

Dormammu - Dormammu rules the Dark Dimension, using his mystical powers to try and conquer other dimensions.

First Appearance: Strange Tales #126

Hulk - When Bruce Banner was exposed to radiation from a gamma bomb, the power of the Hulk was unlocked. Now, whenever Banner gets angry, he becomes the massively strong and powerful Hulk.

First Appearance: The Incredible Hulk #1

Iron Man - Billionaire Tony Stark fights the forces of villainy in the high-tech Iron Man armor. He is one of the cornerstones of the Super Hero community and a founding member of the Avengers.

First Appearance: Tales of Suspense #39

Magneto - With almost complete control of magnetism, Magneto is one of the most powerful mutants alive. He uses his massive powers to fight for his own mutant agenda at any cost.

First Appearance: The X-Men #1

M.O.D.O.K. - M.O.D.O.K., the Mental Organism Designed Only for Killing who leads Advanced Idea Mechanics, is gifted with super intelligence and psionic power, using these powers to vex the world's Super Heroes.

First Appearance: Tales of Suspense #93

Pheonix - Mutant Jean Grey became the receptacle for the powerful Phoenix Force, which grants Jean near god-like powers when it becomes fully active.

First Appearance (as Jean Grey): The X-Men #1

Sentinel - Invented by Dr. Bolivar Trask, Sentinels have one purpose...to destroy or capture mutants. There have been many different types of Sentinels employed by different groups.

First Appearance: The X-Men #14

She-Hulk - When Jennifer Walters received a blood transfusion from her cousin Bruce Banner, she gained the power to become She-Hulk.

First Appearance: The Savage She-Hulk #1

Shuma-Gorath (DLC ONLY) - Shuma-Gorath is an ancient and terrible being who wants to enslave humanity with his supernatural powers and ability to shapeshift.

First Appearance: Marvel Premiere #5

Spider Man - When a radioactive spider bit Peter Parker, he gained the proportionate strength and agility of the arachnid, which he now uses to fight evil.

First Appearance: Amazing Fantasy #15

Storm - Ororo Munroe was gifted with the mutant ability to control weather. She joined the X-Men and has been one of their most reliable members.

First Appearance: Giant Size X-Men #1

Super-Skrull - The Super-Skrull (also know as Kl'rt) was given all of the powers of the Fantastic Four. He uses these powers as a champion of the Skrull Empire.

First Appearance: Fantastic Four #18

Taskmaster - Taskmaster has photographic reflexes, which allow him to copy any movement he has seen perfectly. He uses his abilities as a mercenary working for the highest bidder.

First Appearance: The Avengers #195

Thor - The God of Thunder wields the mighty hammer Mjolnir to fight the forces of evil. He is also a founding member of the Vengadores.

First Appearance: Journey Into Mystery #83

Wolverine - This Canadian member of the X-Men is the best there is at what he does, with his healing factor and adamantium claws. But what he does isn't very nice.

First Appearance: The Incredible Hulk #180

X-23 - A female clone of Wolverine, X-23 has all of his powers in female form.

First Appearance (TV): X-Men: Evolution ("X-23")

First Appearance (Comic): NYX #3

Capcom

Akuma - This warrior values strength over all else, going so far as to abandon his own humanity as a means to obtain more. It is thought that the Buddhist beads around his neck represent warriors who have fallen before him.

First Appearance: Super Street Fighter II Turbo

Amaterasu - The wolf incarnation of the Sun Goddess. She uses her power to restore peace and beauty to the lands.

First Appearance: Okami

Chun-Li - An undercover Interpol detective with lightning fast kicks, Chun-Li seeks to avenge her father's death.

First Appearance: Street Fighter II

Dante - Dante is a mercenary dedicated to vanquishing demons, which were responsible for killing his mother and corrupting his brother. He is also half demon himself.

First Appearance: Devil May Cry

Felicia - A cat woman raised by nuns, Felicia left the convent and is on a quest to become a star.

First Appearance: Darkstalkers

Haggar - Mike Haggar is a former wrestler and mayor of Metro City. He often takes to the street to deal with Metro City's gang problem.

First Appearance: Final Fight

Hsien-Ko - In a Darkstalker attack on their village, Hsien-Ko’s mom gave her life to save her family. Now, Hsien-Ko and her sister fight to save their mother’s soul.

First Appearance: Darkstalkers

Jill (DLC ONLY) - Jill was one of the members of the S.T.A.R.S Alpha team. She was also one of the few people to escape Raccoon City before it was destroyed.

First Appearance: Resident Evil

Morrigan - A fun-loving succubus, Morrigan is very powerful and prefers to neglect her duties and spend time in the human world.

First Appearance: Darkstalkers

Ryu - Ryu lives only for the fight and seeks opponents stronger than himself. He fights using the art of Ansatsuken as taught to him by his master, Gouken.

First Appearance: Street Fighter

Spencer - Spencer is a bionic operative for a special branch of government. However, the government betrayed him, forcing him to go rogue.

First Appearance: Bionic Commando

Trish - A woman created by a demon to seduce and destroy Dante. However, she ends up aiding Dante on his quest to vanquish demons.

First Appearance: Devil May Cry

Tron Bonne - A pirate and mechanical genius, Tron Bonne uses her servbots to do her bidding.

First Appearance: Megaman Legends

Viewtiful Joe - Sucked into Movieland, Viewtiful Joe fights for truth and justice using the time altering powers of his V-watch, which is activated by the magical phrase "Henshin."

First Appearance: Viewtiful Joe

C.Viper - This worldly 30 year old fighter is a CIA agent. She is also a single mother and her daughter, Lauren, is on her mind at all times.

First Appearance: Street Fighter IV

Wesker - Albert Wesker was part of the S.T.A.R.S. Alpha team. However, he was secretly working for the Umbrella Corporation. He has since betrayed Umbrella and is now working for Tricell.

First Appearance: Resident Evil

Zero - Despite being created by the evil Dr. Wily, Zero fights for good and righteous causes throughout his robotic existence.

First Appearance: Megaman X, Megaman Zero

As of right now this is the FULL Character List for Marvel Vs Capcom 3. There could be many more DLC and unlockable characters in the future. 

Source : http://marvelvscapcom3.com/us