Warning: This list contains spoilers for Spider-Man: No Way Home and Hawkeye.
The MCU, like Marvel Comics, is full of iconic characters who are usually the center of attention. Even assembled with dozens or hundreds of other people, Captain America or Spider-Man take centerstage. But the MCU is also stacked with side characters who carry a lot of that same big character energy and are as charismatic and compelling as the heroes topping the credits.
2021 in particular was a standout year for side characters, who often stole the show in their respective properties. Side characters like Agatha Harkness and Yelena Belova made instant impressions in their debuts, and in Agatha's case, essentially took over the show in a meta sense. Many of these side characters will either star in their own MCU series or certainly will in the future.
Katy
Shang-Chi and the Legend of the Ten Rings introduces a broad array of new characters, and by far the most captivating is Katy. Awkwafina brings a lot of charm and charisma to her role as Shang-Chi's friend. She's more than a friend, ultimately becoming a key player in the final battle.
Katy's humor and magnetic personality make her an integral part of the movie, and her journey from a somewhat aimless valet to a proven warrior is as strong and interesting as Shang-Chi or any other main character.
Peggy Carter
Peggy Carter's entire journey in the MCU is a testament to the fact that she's a side character with main character energy. Peggy takes charge in every situation she's in, from chasing after Hydra agents to challenging outdated notions. She's a natural leader and magnetic presence in her many appearances.
She would eventually become the main character in her own series, Agent Carter, and started a new journey where she is the main character as Captain Carter, one of the best versions of Captain America, via the multiverse in the What If..? series.
Luis
Luis is a natural storyteller and perhaps the best example of his ability to take command of the stage is his hilarious recaps in the Ant-Man movies. Luis brings great comic energy to the recaps, which often spin the story in unique and different ways.
Luis also runs the X-Con Security Consultants, making him an essential part of the caper aspect of the movies. In both of his movie appearances so far, he brings a lot of energy and excitement to his part of the story.
Colleen Wing
Colleen Wing is a side character from the Iron Fist Marvel Netflix series who displayed a natural grace and power that made her instantly compelling. Thanks to Jessica Henwick's standout performance, she became such an important part of the series she actually gained the power of the Iron Fist.
Colleen arguably was the best thing about the series, and she would become an important part of the crossover Defenders series and could potentially return to the MCU. Henwick has been very open about the prospect of reprising Colleen in recent interviews.
Ned Leeds
Ned Leeds is a classic side character in the MCU Spider-Man movies, and by his own admission, the quintessential Chair Guy. But Ned's enthusiasm and ability to help his friend and others give him a lot of main character energy.
Ned's story even begins to take on main character vibes in Spider-Man: No Way Home, where he displays some proficiency in magic and also wears the Cloak of Levitation. This hints at some very intriguing possibilities for Ned in the future.
MJ
Comic book fans know Mary Jane Watson is a hero in her own right. Her MCU counterpart, MJ, also has a lot of main character energy. MJ slowly comes to the fore through the MCU Spider-Man trilogy, with her compassion and intelligence making her a key player in the MCU.
She's not only significant to Peter Parker but her faith and trust in him prove integral in the plot of the new movie. Without her dedication to the heroism of Spider-Man, Peter might have opted out of his duty to help the villains at any point.
Darcy Lewis
Darcy Lewis has been most often the assistant of Jane Foster in the MCU, but her hilarious personality often makes her the center of attention. She's also extremely intelligent and dedicated to helping others, which made her a key player in WandaVision.
Darcy is always going to be at the center of any conversation she's in due to her quick wit and magnetic personality, and though she hasn't been the star of the show yet in the MCU, she very easily could be as her story goes forward.
Yelena Belova
Yelena Belova is a side character in both Hawkeye and Black Widow, but she arguably steals the show in both. Florence Pugh delivers a hilarious and infectious performance with many great and funny quotes fans love, giving fans a character who is both silly and scary at the same time.
Yelena forms an instant and electric bond with Kate Bishop in some of the best moments of the Hawkeye series, showing that either one or both can lead and probably will either in a second season of the show or a Black Widow sequel.
Agatha Harkness
Agatha Harkness is perhaps the ultimate version of a side character becoming a main one in the MCU. Agatha literally and figuratively takes over WandaVision in the closing minute of episode 7, transforming the series into her own entitled "Agatha All Along."
Agatha is one of the most powerful magicians in the Marvel Universe, and thanks to the series, one of the most popular. She emerges from her role as a side character in WandaVision to the star of her own show in the near future, Agatha: House Of Harkness.