Warning: This list contains spoilers for Doctor Strange 2!
MCU movies and TV shows keep on introducing new characters from one dimension or planet, recently doing so in a shocking manner during Doctor Strange in the Multiverse of Madness. At the same time, some of the recent additions to the Universe have reintroduced a few characters whom viewers had presumed were dead. For instance, old Captain America foes acquired new forms, appearing years after their death in the Second World War.
Then, there are some minor and supporting characters whom fans would have never thought to have an increased role in future MCU originals. To put it in a nutshell, there's a plan for almost every Marvel character's resurgence.
Red Skull - Avengers: Infinity War
Red Skull has been Captain America's arch-nemesis for a long time. So, it wasn't surprising to find Hugo Weaving playing the iconic Captain America comic book villain in Steve Rogers' origin story. However, after The First Avenger, fans caught an unexpected peek of Red Skull in Infinity War.
Appearing as a floating spirit of sorts, Red Skull served as a"stonekeeper," guarding the Soul Stone on the planet of Vormir. It seemed strange for the Nazi villain to pop up in the middle of nowhere but it makes sense as he himself had lusted for the power of Tesseract, an act that cursed him in this new role.
Dr. Arnim Zola - Captain America: The Winter Soldier
Red Skull's trusted scientist and HYDRA accomplice Arnim Zola might have a meek physical appearance but he is quite the mastermind. While Captain America survived the decades after 1945 while staying frozen underground, the late Zola succumbed to a terminal illness in the 1970s.
And yet, actor Toby Jones voiced the character in a surprise cameo in The Winter Soldier. Apparently, Zola had transferred his intelligence to a computer system. Even in the 21st century, Zola proved to be intimidating as he intentionally distracted Captain America and Black Widow for HYDRA to attack the base and erase all covert information.
Abomination - Shang-Chi And The Legend Of The Ten Rings
Tim Roth's Abomination in The Incredible Hulk was quite menacing but he soon faded into obscurity with the antagonists introduced in the subsequent movies. Hulk changed a lot since Phase 1, affecting the longevity of the movie further. Hence, it was a pleasant surprise to find Abomination returning in a more comic-accurate form more than a decade later in Shang-Chi.
Even though he just appears in a memorable fight scene with Wong, he is all set to have a much larger role in the Universe as can be seen from the recent She-Hulk trailer.
Monica Rambeau - WandaVision
As Captain Marvel was set in the 1990s, most of the characters barring Nick Fury and Phil Coulson were new to the movie-going audiences. Monica Rambeau's mother Maria played a more pivotal role as Carol Danvers's best friends and a fellow pilot. And as Danvers still continued to hold the mantle of Captain Marvel in present-day movies, a now-adult Monica wasn't likely to be the second Captain Marvel as has been the case with her comic book counterpart.
It was interesting to find a more original storyline for her in WandaVision as she now plays the role of a S.W.O.R.D agent. With her determination to investigate Wanda's self-created Utopia in New Jersey, she definitely turned out to be one of the best WandaVision characters. Her mother's return in the Doctor Strange sequel was also unexpected.
Ulysses Klaue - Black Panther
As an illegal exporter of Wakandan vibranium, Ulysses Klaue makes a brief appearance in Avengers: Age of Ultron. With vibranium being name-dropped, it was certain that Black Panther would be introduced in the MCU in a matter of a few years. And when it did happen, it was amusing to see Andy Serkis reprise his role as Klaue.
Of course, the spotlight was on Michael B Jordan's Killmonger who was widely regarded as one of the best MCU villains. At the same time, Serkis got to play Klaue in all his manic glory for the limited screentime he got. For fans of Serkis' body of work, this role was also amusing as it is easily a rare sight to find him in a big-budget production without him playing a live-action character.
Trevor Slattery - Shang-Chi And The Legend Of The Ten Rings
The big reveal in Iron Man 3 polarized fans to a great extent. Some were in awe of Sir Ben Kingsley's duality as the menacing "pseudo-Mandarin" and the relatively harmless Trevor Slattery while others were just dissatisfied with the plot twist. Even though Slattery did make another MCU appearance with the short All Hail The King, nobody would have guessed that he will go on to appear as the court jester of the real leader of the Ten Rings.
Kingsley's character is still powerless unlike the lethal facade that he had once put on. And yet, it is delightful to see him aid Shang-Chi and his allies. His friendship with the creature known as Morris is another added bonus.
Darcy Lewis - WandaVision
When it comes to Kat Dennings' best TV shows, 2 Broke Girls was probably her most famous credit before her unexpected role in WandaVision marked a resurgence in her popularity. Playing the scientist Darcy Lewis in Thor and The Dark World, it is only natural to expect her to appear in future Thor projects. But ever since Darcy's good friend Jane Foster broke up with Thor, she too didn't make an appearance in Ragnarok.
But her pivotal part in WandaVision goes on to show how Darcy can shine as a standalone character without any direct links to Thor. The shared universe concept of the Marvel films hence allows such supporting characters to stand out on their own in properties associated with different superheroes. She was also a highlight of WandaVision.
Howard The Duck - Avengers: Endgame
Back when the MCU wasn't a concept and standalone Marvel movies were more common, Howard The Duck starred in his own titular adventure in 1986. Ever since that commercial failure, Howard never appeared in any other Marvel film until a surprise post-credits scene in Guardians of the Galaxy. Viewers would have thought this is just a fun Easter Egg and a relatively hilarious and unimportant superhero like the talking duck wouldn't appear again.
In another equally amusing cameo, Howard returned in Endgame along with the rest of the Marvel heroes. Even though he might not be that powerful at all, he still wields a gun and is willing to fight Thanos and his minions. In What If, Howard has made even wilder appearances such as the one episode in which he ends up marrying Darcy Lewis.
Black Bolt - Doctor Strange In The Multiverse Of Madness
The Inhumans were set within the same universe as MCU movies but the show was panned. So, nobody ever expected another appearance but they got one in Doctor Strange in the Multiverse of Madness. Appearing alongside other members of the Marvel comic book team Illuminati, like Professor X and Mr. Fantastic, Anson Mount's Black Bolt (introduced as the Earth-838 version of the character) returns for a memorable cameo.
As he attempts to use his highly destructive shockwave of a voice, Wanda seals his mouth shut resulting in his head exploding. As this version of Black Bolt is no more, the character's fate in future MCU movies is uncertain.
Harley Keener - Avengers: Endgame
Hailing from Tennessee, young Harley Keener's Christmas wasn't marked by Santa's visit but a surprise intrusion by Tony Stark in Iron Man 3. Helping an injured Tony fix his armored suit, they end up striking an unlikely friendship. However, as Keener doesn't have any superpowers or any comic book connections, he seemed like a one-time character.
But a much older Keener makes an appearance in Tony Stark's funeral towards the final scenes of Endgame. This makes for a perfect cameo to show the impact that a man like Stark had on the rest of humanity in general and people like Keener in particular. Bullied in school and abandoned by his family, Keener saw Stark as a father-like figure making this cameo much more personal than expected.