Dr. Leonard Samson
In the comics: After creating a cathexis ray projector that would drain off gamma particle and psionic energy from Bruce Banner into a cure for Betty, most of that psionic and gamma energy that was drained from Banner stayed within the ray projector. Overcome with curiosity, and perhaps a desire to gain superhuman powers himself, Samson irradiated himself with those energies within the projector, resulting in the slim, brown-haired psychiatrist being transformed into a green-haired, muscle-laden superhuman with gamma-boosted strength.
In the movies: Dr. Leonard Samson is a psychotherapist who works at Culver University. He became romantically involved with Betty Ross for a time; however, when Bruce Banner returned from hiding and came back into Ross' life, Samson became jealous and called Thaddeus Ross to have Banner arrested, putting the relationship between him and Betty at standstill.
While not much has been said about this minor character in the MCU since The Incredible Hulk, I imagine there is still potential for him to be used in some capacity in the future as "Doc" Samson.
In the comics: One evening, as Samuel Sterns was moving canisters of waste materia, one of the containers broke open dousing him in gamma radiation. Sterns survived, but not without cost -- he discovered that his intellect had increased a thousand-fold, retaining information with the accuracy of a computer; however, his gamma-irradiated body mutated his skin permanently green and his head increased in size.
In the movies: Samuel Sterns is a cellular biologist and Grayburn College professor who was helping Bruce Banner find a cure to rid him of the Hulk. When Banner's blood got into an open wound in his head, his mind suffered a rapid mutation which greatly increased his mental abilities. Later found by Natasha Romanoff, who had a brief dialogue with him, Sterns was able to identify Black Widow's birth place from the incredibly small accent in her voice. Sterns attempted to bribe her with promise of returning her to Stalingrad to no avail, as Widow shot him the leg and arrested him (in "Fury's Big Week").
The potential for Samuel Sterns returning as The Leader in the future of the MCU is huge. I could see him escaping custody and attempting his own world takeover as we head into Phase 4. Tying in with The Thunderbolts, Red Hulk, and/or some version of Hulk and the Agents of S.M.A.S.H. Perhaps this could explain the cancelation of Inhumans?
In the comics: Amadeus Cho, son of Helen Cho, is a supporting character of both Hulk and Hercules with the nickname Mastermind Excello.
In the movies: Amadeus Cho, a student at Culver University, is one of the smartest students in his class. He worked in the computer class by night, granting a "disguised" Bruce Banner access to the computers in exchange for some pizza.
Did you see the Helen Cho connection? They are slowing building something for Bruce Banner and his secondary characters, even with the semi-confusing solo-Hulk rights belonging to Universal.
The Original Human Torch
In the comics: The original Human Torch (not from the Fantastic Four) is a Synthezoid, or biological android, with the abilities of flight and flame control, meaning it can ignite its own body to become essentially invulnerable.
In the movies: In Captain America, during the Stark Expo, it's presented in an oxygen deprived glass tube. It's unknown if it's operational, or ever was, but present in the MCU nonetheless.
In the comics: Adam Warlock is an artificially created human who was born in a cocoon at a scientific complex called The Beehive in order to create and exploit the perfect human. Most people on Earth are unaware of Warlock's existence.
In the movies: The Cocoon is one of the items obtained by Taneleer Tivan and stored in his museum. Present in the museum both when Sif and Volstagg delivered the Aether at the end of Thor: The Dark World and in Guardians of the Galaxy when they attempted to deliver the Orb, you know... before Tivan's assistant (Carina) unleashed the power of the stone within the Orb (Power Stone). Some time after the explosion, the Cocoon is shown to have opened.
Before arguing with me on this, let's just remember the initial rumor of the cocoon was confirmed by James Gunn to be Adam Warlock's. And you thought this was just some random after-credits' scene with Howard the Duck? Think again.
That's an opened cocoon to the left of Howard. I will be shocked if Adam Warlock isn't introduced in Guardians of the Galaxy, Vol. 2.
In the comics: Christine Everhart works as a reporter for The Daily Bugle and has investigated Tony Stark/Iron Man on multiple occasions.
In the movies: You might remember Christine Everhart from Iron Man and Iron Man 2 as the investigative journalist who worked for Vanity Fair. Now, for those of you that have kept up with the viral promotions from the past few Marvel films, Everhart is an anchor for WHiH World News.
In the comics: The robotic bride of her creator Ultron, who, much like Vision, betrayed him after seeing his evil and became a member of the Avengers.
In the movies: J.O.C.A.S.T.A. is a back-up U.I. program created by Tony Stark. Instead of choosing J.O.C.A.S.T.A. to replace J.A.R.V.I.S., who had been uploaded into Vision, Stark opted to choose F.R.I.D.A.Y. instead.
In the comics: Ted Sallis, the alter-ego of the Man-Thing, was a professor at Empire State University and married to Ellen Brandt (who eventually betrayed him to A.I.M.).
In the movies: Man-Thing was among the many creatures being observed by S.H.I.E.L.D. before the HYDRA Uprising. He is briefly mentioned, during an episode of Agents of S.H.I.E.L.D. (season 1, episode 20), during a phone conversation between Pepper Potts and former S.H.I.E.L.D. Deputy Director Maria Hill as she was leaving a Congressional hearing. Hill asked Potts, "Who or what is a Man-Thing?"
The inclusion of Ellen Brandt as an agent of A.I.M. and one of the volunteers to be injected with the Extremis virus in Iron Man 3, is another indication of Man-Thing's presence.
In the comics: Namor was born the first known Human/Merman hybrid, with a human father and Atlantean mother. The young prince grew to have a short, nasty temper and a hostile attitude toward humans, blaming them for the near-destruction of Atlantis. Later, becoming King Of Atlantis, Namor has been seen as both a friend and enemy, at different times serving with the X-Men (being a mutant, as well), Illuminati, Defenders, Invaders, and Avengers, at different times.
In the movies: This one is a little more complicated than it seems at first glance. From what I've read, Universal owns the movie rights to Namor and as a half-mutant, I'm not sure where or how he technically falls into the whole movie-rights-game between Marvel, Fox, and Universal.
Many have speculated that the bottom circle on the map (above) is Atlantis, but if you compare the movie image to the comic's map of Atlantis (below) and it's surroundings, it actually shows that the area is Namor's "Fortress of Solitude," while the boundaries of Atlantis itself appears to be a rather large area located off the Western coast of Europe.
Which character did you forget about?
Sources: Marvel.com, marvelcinematicuniverse.wikia.com