Captain Marvel introduces MCU fans to a new cast of characters that only fans of the Marvel Comics will likely know. One of those is Monica Rambeau (played by Akira Akbar), the 11 year-old daughter of Carol Danvers' (Brie Larson) best friend and fellow U.S. Air Force pilot Maria Rambeau (Lashana Lynch). While the kid is a supporting character in the movie, a lot happens to Monica Rambeau in the Marvel comics, and she's just as important to Captain Marvel's history as Carol is. In fact, the comics version of Monica carried the Captain Marvel mantle before Carol Danvers did, in the 1982 comic Amazing Spider-Man Annual Vol 1. 16.
Monica is the second superhero to go by the name Captain Marvel — after the Kree warrior Mar-Vell. So some fans are already speculating that Monica Rambeau could become the next Captain Marvel onscreen whenever Larson finishes her turn with the role. That may seem like looking way far into the future, but the timeline of Captain Marvel plays an important role in figuring this all out. The new superhero movie takes place in the mid-'90s, so really, when Captain Marvel shows up in the next Avengers movie, Endgame — out April 26 — the young Monica Rambeau you see in Captain Marvel would be in her mid-30s. That's not to say that Monica will replace Carol as Captain Marvel in Avengers: Endgame, but it could happen eventually due to the former's comic book history.
As mentioned before, Monica first appeared in the comics in 1982 when, Monica served as a lieutenant for the New Orleans harbor patrol. A special mission involving an "other-dimensional energy-tapping device" leads Monica into a mishap with the machine that leaves her with superpowers, including the ability to convert her own body into powerful energy. From there, Monica becomes Captain Marvel, and she leads a long-spanning comic book career which involves her joining the Avengers for numerous missions.
Monica's Captain Marvel was the first female African-American Avenger, so she's already made history. In fact, Monica even became the leader of the Avengers at one point after the Wasp stepped down, for which Captain America had nominated her.
In the '90s, Monica's title as Captain America is disputed by Mar-Vell's offspring, Genis, which leads her to change her superhero name to Photon. After that, Monica adopts the codename Pular before going by Monica Rambeau, and finally choosing the superhero title Spectrum. Currently in the comics, Monica's Spectrum is a member of the team, the Ultimates, which includes Black Panther, Blue Marvel, Ms. America (America Chavez), and Captain Marvel (Carol Danvers). See, after Monica gave up the title as Captain Marvel to Genis, Carol Danvers adopted it herself in 2012 — according to Polygon, Carol is the sixth superhero to use the name.
Should Monica show up in later MCU movies that take place in the present day, she could easily be either a new Captain Marvel or her current comic book character, Spectrum. In an interview with Rotten Tomatoes, Lynch implied that her movie daughter Monica could have a bigger part as a superhero in future films. "I feel like there’s, there’s always some things in the works when it comes to the MCU, and there’s always things changing. They go by the comics, but they also switch things up sometimes to keep us on our toes, to keep us excited," she said.
Considering that Monica Rambeau's Spectrum can actually become ultralight radiation, the impressive superhero seems bound to show up in future MCU movies, whether it be in Phase 4 or beyond. What you see of Monica in Captain Marvel is probably just the character's beginning.