It's not just the powerful stars that make the Marvel Cinematic Universe movies the force it is at the box office -- Thor, Iron Man, Captain America, the Incredible Hulk, the Black Panther, and so on -- but how they work together. The more we see them, the more we want to see them. We're not just talking about the big team-up films like The Avengers, Guardians of the Galaxy and Captain America: Civil War; it's exciting to see a character pop up in other films they aren't headlining in, like Iron Man in Spider-Man: Homecoming, or Bruce Banner in Iron Man 2, or Doctor Strange in Thor: Ragnarok, or The Falcon in Ant-Man.
But there's another side to the pleasure of seeing popular characters; it's the frustration that comes with other appearances that are wasted. Some characters are there as Easter eggs for avid fans of the comics. Others seem to be there to plant the seeds for more adventures, but those story threads aren't weaved into the whole. Some show up once and are forgotten, never to be seen again. Others are presented as if they're the next big thing, but the execution is lacking or the ball gets dropped and they don't catch on, regarded like unwelcome relatives at the family picnic.
20 THE INHUMANS
The Inhumans first appeared in Fantastic Four #45 (December 1965) and bounced around as guest characters and in backup features for years. As headliners, their record isn't much better, with a spate of short-lived ongoing series, several miniseries and the occasional graphic novel.
Still, the Royal Family of Attilan got their shot as headliners in prime time TV. ABC did the pilot in a big way, presenting it as an IMAX film before it put it on the air Sept. 29, 2017. But fans complained about the quality of the IMAX conversion and the special effects, and critics weren't kind. The show limped through eight episodes and ABC canceled it in May. The Internet Movie Database now lists The Inhumans as a miniseries.
19 AGENT CARTER
Peggy Carter has been someone special to Captain America since his days in World War II. She debuted in Tales of Suspense #75 (March 1966). Initially identified as the older sister of S.H.I.E.L.D. Agent Sharon Carter in Captain America (Volume 1) #161 (May 1973), she was retconned to be her aunt.
In the Marvel Cinematic Universe, Carter first appeared in Captain America: The First Avenger (2011). She guested in Agents of S.H.I.E.L.D. in 2014 and led Agent Carter for two seasons in 2015-2016. She also had cameos in Avengers: Age of Ultron and Ant-Man, both in 2015. But she dies in Captain America: Civil War (2016), and there don't seem to be any plans for her.
18 JANE FOSTER
Jane Foster was Thor's love interest in 2011's Thor. In the film, she's an astrophysicist doing research on wormholes. This is a significant upgrade from her initial incarnation in comics as a nurse and chronic damsel in distress, beginning with her first appearance in Journey Into Mystery #84 (September 1962).
Foster figured prominently in Thor and its first sequel, Thor: The Dark World (2013). But she was conspicuously missing from The Avengers (2012), with her absence explained in a passing line of dialogue. She also wasn't in Avengers: Age of Ultron (2015). In Thor: Ragnarok (2017), we learn that she and Thor are no longer a couple, thanks to Thor's efforts to find the Infinity Stones.
17 THE MANDARIN
Fans squawked long and loud over the version of the Mandarin presented in Iron Man 3 (2013). In the comics, the Mandarin is one of Iron Man's oldest adversaries, whose magic-based powers contrast with Iron Man's high-tech gear. He first appeared in Tales of Suspense #50 (February 1964).
In Iron Man 3, the Mandarin initially appears to be the formidable foe comics fans were expecting. But he was revealed to be Trevor Slattery, a washed-up actor hired by the movie's true villain, Aldrich Killian, to pose as the menacing leader of the outlaw group the Ten Rings. That fake-out didn't go over well with viewers.
16 THE HUMAN TORCH
It was a nice little Easter egg for fans watching Captain America: The First Avenger (2011). During a scene where young Steve Rogers visits the 1943 Stark Expo, we see a large glass case bearing the legend "Dr. Phineas Horton Presents the Synthetic Man." Within is a man wearing a red unitard.
Comics fans know that when that man within is exposed to air, he bursts into flames, becoming the Human Torch, a Golden Age character who debuted in Marvel Comics (Volume 1) #1 (1941). But that moment doesn't happen in The First Avenger, or in any of the other MCU films. We don't know if we ever will see the Torch on screen.
15 THE ABOMINATION
The Abomination first appeared in comics in Tales to Astonish #90 (April 1967). He was Emil Blonsky, a Soviet spy who infiltrated a U.S. Air Force base in New Mexico. Blonsky activated a machine that bombarded him with a concentrated dose of gamma radiation, and became a big, ugly bruiser who rivals the Hulk in strength and meanness.
In The Incredible Hulk (2008), Blonsky was a test subject for an attempt to recreate the Super-Soldier Serum that gave Captain America his abilities. Greedy for power, he also insisted on being injected with a sample of Bruce Banner's gamma-irradiated blood. The combination transformed Blonsky into the Abomination, and he and the Hulk fought through Harlem before he was defeated. He hasn't been seen since.
14 MOCKINGBIRD
Barbara "Bobbi" Morse, Mockingbird, moved from bit player to S.H.I.E.L.D. agent to Avengers member in her history in comics. She first appeared in Astonishing Tales #6 (June 1971), ultimately becoming Mockingbird in Marvel Team-Up #95 (July 1990).
Mockingbird joined the ABC TV series Agents of S.H.I.E.L.D. in its second season, after an attempt to put the character in a solo show on ABC Family in 2011 failed. On Agents of S.H.I.E.L.D., Mockingbird was often partnered with her ex-husband, Lance Hunter. Their chemistry sparked interest in a spinoff featuring the two of them, titled Most Wanted. Accordingly, they were written out of Agents of S.H.I.E.L.D., but ABC didn't order the series.
13 BETTY ROSS
Betty Ross was a key part of Bruce Banner's life, from issue #1 of The Incredible Hulk (May 1962). The daughter of Hulk antagonist Gen. Thaddeus "Thunderbolt" Ross, Betty Ross loved and protected Banner in both of his guises, through thick and thin, marriage and death, and even becoming a Hulk herself.
In The Incredible Hulk (2008), Betty Ross was a fellow scientist at Culver University working with Banner on an attempt to replicate the Super-Soldier Serum. The experiment failed, turning Banner into the Hulk. Ross aided Banner while he was on the run, but she hasn't appeared in or even been mentioned in any of the subsequent Marvel Cinematic Universe films.
12 ERIK SELVIG
Dr. Erik Selvig first appears in Thor (2011), an astrophysicist researching wormholes with fellow astrophysicist Jane Foster and research assistant Darcy Lewis in New Mexico. The three find Thor in the desert moments after he arrived on Earth, after he was banished from Asgard, and help him recover Mjolnir and battle Loki, who has usurped the throne of Asgard.
Selvig also appears in Avengers (2012), as S.H.I.E.L.D. hires him to discern how the Tesseract works. He features prominently in Thor: The Dark World (2013) and is in Avengers: Age of Ultron (2015). But he is not in Thor: The Dark World (2013) or Avengers: Infinity War (2017).
11 LAURA BARTON
Hawkeye has always seemed overmatched in the massive Avengers battles, while they are fighting for massive stakes -- saving the world in Avengers (2011) or Avengers: Age of Ultron (2015). But when they are fighting for all of existence in Avengers: Infinity War (2018), Hawkeye is noticeably absent.
That's because Hawkeye is a smaller-scale hero fighting for something more personal: His family. In Age of Ultron, we learn that Hawkeye has a wife, Laura, and two children, Cooper and Lila, who stay on a secret homestead that's off the grid. This is the only time Laura Barton and the children were in a Marvel Cinematic Universe film. A line of dialogue in Infinity War tells us Hawkeye is under house arrest.
10 LANCE HUNTER
Mercenary Lance Hunter was recommended for S.H.I.E.L.D. in the second season of Agents of S.H.I.E.L.D. by agents Isabelle Hartley and Bobbi Morse, also known as Mockingbird. We learn that Morse is Hunter's ex-wife, leading them to bicker quite often as they worked together. Producers made plans to spin off Hunter and Mockingbird into their own show, but the project fell through the cracks.
In the third season, they tried again for a spinoff, writing Hunter and Mockingbird out of the show by having them get disowned by the agency and go on the run. However, the pilot for the spinoff, Most Wanted, never aired and ABC didn't pick up the series.
9 THE ABSORBING MAN
Carl "Crusher" Creel was a villain who frequently fought Thor, but also was in several versions of the Masters of Evil. An ex-boxer, Creel's first appearance was in Journey Into Mystery #114 (March 1965). Thanks to a magic potion provided by Loki, Creel gained the power to absorb the properties of whatever he touches.
Creel showed up in the second season of Agents of S.H.I.E.L.D., as a HYDRA recruit, and appeared occasionally in subsequent seasons. He met his seeming end in the fifth season, absorbed into the Gravitonium by Glenn Talbot. Creel also is cited in a first-season episode of Daredevil, in a flashback where he is mentioned as an opponent of "Battlin' Jack" Murdock, Daredevil's father.
8 DEATHLOK
Deathlok debuted in comics in Astonishing Tales #25 (August 1974). He was Luther Manning, a physically damaged soldier who was re-animated as a cyborg by Simon Ryker about 15 years in the future, which then was 1990. Other people have taken on the Deathlok persona since then.
On television, Deathlok is Mike Peterson, who appeared in the first episode of Agents of S.H.I.E.L.D. He was hurt on his job and accepts an offer to take the Centipede Serum to heal. But he didn't know that Project Centipede was an offshoot of HYDRA, which took him and converted him into a cyborg. S.H.I.E.L.D. rescued Peterson, and he worked with them covertly against HYDRA. At one point, HYDRA took him again and removed the cybernetic parts.
7 DOC SAMSON
Psychiatrist Leonard Samson first appeared in The Incredible Hulk (Volume 2) #141 (July 1971), finding a way to cure Betty Ross, who had been turned into crystal. Samson devised a way to siphon gamma particles and psionic energy from Bruce Banner, which cured him from being the Hulk, and trained it on Ross, which cured her. Samson later turned the device on himself, and gained extra muscle, superstrength and green hair.
There was no hint of that in The Incredible Hulk (2008). In the movie, Leonard Samson is Betty Ross' romantic partner, but when Bruce Banner returns to her after five years on the run, Samson called Gen. Thunderbolt Ross to have Banner captured. Samson hasn't been in any other Marvel Cinematic Universe movies.
6 DARCY LEWIS
Darcy Lewis first appears in Thor (2001). Although she is a political science major, she became the assistant to astrophysicists Jane Foster and Erik Selvig on their research into wormholes. While in New Mexico, the trio encounters Thor, who had been banished from Asgard, and help him retrieve his hammer, Mjolnir.
Lewis also appears in Thor: The Dark World (2013). She helps bring Selvig to safety after he has a mental breakdown caused indirectly by the Convergence, an alignment of the Nine Realms. Lewis helps Selvig and Foster aid Thor in defeating the Aether, a force unleashed by Malekith to destroy the Nine Realms. That was the last time we saw Lewis in a Marvel Cinematic Universe film.
5 THE TINKERER
The Tinkerer, who first appeared in print in Amazing Spider-Man #2 (May 1963), is a genius engineer and inventor who makes gadgets and gear for supervillains. In his early career, he hid his identity by pretending to be a space alien.
He appears in Spider-Man: Homecoming (2017) using his real name, Phineas Mason. He works with the salvage crew led by Adrian Toomes, which was contracted after the Battle of New York to clean up the city. Toomes sought revenge after his company was forced off the job by the Department of Damage Control. Toomes pressured Mason into creating an exo-suit from Chitauri technology with flight capability. Spider-Man defeated Toomes, but we never saw what happened to The Tinkerer.
4 BLIZZARD
On Agents of S.H.I.E.L.D., Donnie Gill was a S.H.I.E.L.D. recruit to its Academy of Science and Technology. In the episode "Seeds," Gill and cadet Seth Dormer build a device to manipulate weather, but lose control of it. It creates a blizzard that kills Dormer, and Gill develops the power to freeze things with a touch.
In "Making Friends and Influencing People," Gill is brainwashed by HYDRA and they and S.H.I.E.L.D. fight for control of his mind aboard a ship. Gill is shot and falls overboard; his body was not found. Blizzard first appeared in comics in Iron Man #223 (October 1987), although there was another, Gregor Shapanka, who had the name and powers. Shipanka first appeared in Tales of Suspense #45 (September 1963).
3 THE LEADER
The Leader first appeared in comics in Tales to Astonish #62 (December 1964). He was Samuel Sterns, a chemical plant worker exposed to gamma radiation when containers of radioactive material he was moving exploded. He transformed into a green-skinned being with a giant cranium and intellect to match.
In The Incredible Hulk (2008), Sterns was a cellular biologist who worked with Bruce Banner to cure his transformations into the Hulk. But Emil Blonsky, who already was treated with the new Super-Soldier Serum, forces Sterns to inject him with Banner's blood. The combination turns Blonsky into the Abomination. Some of Banner's blood splashes into a cut on Sterns, causing him to change. S.H.I.E.L.D. captured him, and Sterns hasn't been seen since.
2 CHRISTINE EVERHART
Christine Everhart was an investigative reporter for the Daily Bugle newspaper in Iron Man (Volume 3) #75 (February 2004), covering Tony Stark's testimony before the U.S. Senate. She appears in Iron Man (2008) as a Vanity Fair reporter who questions Stark about his company's munitions manufacturing, accusing him of "war profiteering." Stark, while flirting with Everhart, defends his company as one that also makes medical technology and "intelli-crops."
In the next scene, they sleep together; in the morning, Stark's assistant, Pepper Potts, kicks her out. Everhart also appears in Iron Man 2 (2010), in a party scene. Stark and Potts -- who is now CEO of Stark Industries -- make veiled digs at Everhart as she is introduced by business rival Justin Hammer.
1 WORLD SECURITY COUNCIL
The World Security Council, which has oversight over S.H.I.E.L.D., first appeared in The Avengers (2012). Its members appeared in shadow, giving orders to S.H.I.E.L.D. Director Nick Fury. Fury pushes back, telling them he's "ignoring" the Council's decision to fire a nuclear missile into the portal where the Chitauri are coming to Earth. At the end, Fury also tells the Council he hasn't retrieved the Tesseract and doesn't know where the Avengers went after the Battle of New York.
In Captain America: The Winter Soldier (2014), the Secretary of the Council, Alexander Pierce, was revealed to be a HYDRA operative who had filled S.H.I.E.L.D. with double agents loyal to HYDRA. Several Council members are eliminated, and the Council has not been part of subsequent films.