The MCU has developed arguably the best superhero world in the world of movies, and now on television with the Disney+ series. Fans almost universally accepted the actors taking on the roles of the main characters, from Robert Downey Jr. and Chris Evans to Chris Hemsworth and Chadwick Boseman.
However, Marvel has also knocked it out of the park with the supporting actors in the movies. Some of these side characters were so great that it seemed they deserved even more prominent roles and more screentime than they received, from the friends of the heroes to fellow heroes and even a surprisingly entertaining villain.
Shuri
Shuri was quickly one of the most entertaining characters in Black Panther. The sister of T'Challa played a significant role as the smartest person in Wakanda and the creator of the tech keeping the country on the cutting edge of the future. She also had a fantastic personality, someone who had no problem talking smack to anyone and never doubting herself. Rumor has it that Shuri will step into the role of Black Panther in the sequel, and she deserves it.
Valkyrie
When Tessa Thompson joined the MCU for Thor: Ragnarok, it ended up as a fantastic addition. She became Valkyrie, completely changing the character from the Marvel Comics in all the best ways. In Thor: Ragnarok and Avengers: Endgame, she proved to be a superior character to the comics. Valkyrie deserves a much more significant role in the MCU. With Thor leaving her in control of Asgard, there are hopes that Tessa Thompson steps up as Valkyrie and continues to grow into a significant part of the upcoming movies.
Wong
There were significant changes to Wong in Doctor Strange. In the comics, he was mostly the servent for Stephen Strange, and while he was able to hold his own in an attack, he wasn't much more than someone who brought Strange tea when he needed it. However, in the Doctor Strange movie, Wong was much more important and was a skilled magic user in his own right. He was there for the final fight in that movie, but he deserves a much more significant role in the future.
Maria Hill
Maria Hill has been around for several appearances in the MCU, but she always appeared as the right-hand of Nick Fury. From her role in Avengers to her appearance in Captain America: Winter Soldier and later in Spider-Man: Far From Home, she was just another underling to Fury.
In the comics, Hill is so much more. She usurps Fury at one point in S.H.I.E.L.D. and is a strong leader in her own right. With Cobie Smulders in the role, she is a character that should be doing so much more in the movies.
M'Baku
Moving back to Black Panther, there was a lot of concern about how the movie would deal with the character of Man-Ape. The good news is that the MCU never used that name and just used his real name of M'Baku, the leader of the more feral tribes in Wakanda. Winston Duke took the role of M'Baku and just blew away everyone with her performance, proving to be on the level of T'Challa as a warrior and someone who needs more screentime in the MCU as soon as possible.
Sharon Carter
Sharon Carter looked finished in the MCU, but Disney+ found a way to add to her role in the movies. In the comics, Sharon and Steve Rogers were a couple for a very long time. However, in the films, she was there alongside Cap, but as an ally and nothing more. That betrays her importance in the comics, and there is a chance the MCU could do right by her with the upcoming The Falcon and Winter Solder Disney+ series, as Emily VanCamp is part of that cast.
Jane Foster
The Thor movies seriously underrepresented the character of Jane Foster. She only appeared in the first two films, and then in Thor: Ragnarok, her name only popped up briefly as breaking up with Thor. It was a total insult for a character that is so important in the comics.
Natalie Portman has commented on her dissatisfaction in her character's portrayal and screentime in the movies, and she has every right to be disappointed. Luckily, it sounds like Jane will be back in full force in the next Thor movie and possibly even wield Mjolnir for the first time in the MCU.
Happy Hogan
Happy Hogan didn't have a massive role in the Iron Man movies for a good reason. Jon Favreau directed the first two films, and it made sense that his screentime was limited. However, he proved in Spider-Man: Far From Home that he is a perfect antithesis for the superheroes, someone who is is supposed to be a strong and powerful character but is often insecure in front of those with extraordinary powers. Happy Hogan was a great character that wasn't used enough in the movies.
Falcon
For a member of The Avengers, Falcon has been almost invisible compared to other members of the team. He first appeared in Captain America: The Winter Soldier, where he mostly served as a sidekick to Captain America. Outside of this, he was part of the battle in Captain America: Civil War and was just a supporting hero in both Avengers: Infinity War and Avengers: Endgame. Luckily, Anthony Mackie will finally get a chance to shine as Falcon in the upcoming Disney+ series.
Klaw
There was also one villain that stole every scene he appeared in but was nothing more than a side character for the shows. This is Ulysses Klaue, portrayed by Andy Serkis. Before this, most people knew Serkis from his roles as Gollum in Lord of the Rings and King Kong. However, in Avengers: Age of Ultron, he played Klaw, a villain working for Ultron. He then was fantastic in Black Panther, once again as a minion for the main bad guy, this time Killmonger. However, he deserved to be a significant player and never got the chance.