WARNING: This article contains major spoilers for Black Widow.
Black Widow revealed how the Red Guardian, Alexei Shostakov, was Natasha Romanoff's 'father' once upon a time. The movie's post-credits scene clearly sets up her sister and fellow Widow Yelena's future in the MCU, but where will the Red Guardian appear next in the franchise? His comic book history points toward many different options.
The Red Guardian has a rich comic book arc involving characters and teams that are already present in the MCU as well as with some that have yet to appear, giving him a lot of places to show up that aren't necessarily a part of the film universe yet. Some of them might involve Alexei Shostakov, or thanks to the multiverse, other versions of the Red Guardian.
Black Widow Sequel
A Black Widow sequel seems likely given the success of the film so far, and so does Red Guardian's return. While Natasha Romanoff has died in the MCU, the movie could go back farther in time to include her again or move forward with Yelena as the Black Widow.
In any case, the Red Guardian would be an obvious character to return along with his love interest and Widow Melina. With Alexei acting as Yelena's frustrating but caring father figure, it could be another fun family adventure.
Hawkeye
Yelena Belova is a lock to appear in the upcoming Hawkeye MCU series, thanks to the mission she was given by one of Marvel Comics' most important spies, the Contessa. It's very possible that the Red Guardian finds his way into the story as well.
If Yelena goes after Hawkeye, that may lead her back to her father, who will also have something to say about it. He could also prove very valuable once Yelena learns the truth about Natasha's death on Vormir and questions about the Contessa's motives emerge.
The Defenders
The Defenders is a team that appeared in the Netflix suite of Marvel shows, and the Red Guardian may be a way to reintroduce them to the MCU proper. While the character first appeared in Avengers #43, another version would become part of The Defenders in the 70s.
Tania Belinskaya is the second version of the character to appear in the comic books. She joins the team as a hero and acts as one of the most powerful members of the Defenders for a number of major story arcs in the late 70s.
The Invaders
Another version of the Red Guardian was associated with another major Marvel superhero team. The first Red Guardian in the chronology of Marvel Comics is Aleksey Lebedev, who fought against the Invaders during World War II.
If the MCU decides to go back to feature the Invaders, who included Captain America, Namor, and the original Human Torch, then the Red Guardian would be a natural character to include in the story, as a hero, villain, or both.
She-Hulk
The Red Guardian has a connection to She-Hulk in the comics that could lead to his appearance in her upcoming TV show. A later version of the Red Guardian known as Anton appeared in the 2008 She-Hulk series.
In the course of the story, She-Hulk clashes with the Winter Guard, the Russian super-team, while trying to help a country that has been devastated by an earthquake. The two characters eventually call a truce, and this could be a comic book storyline that the She-Hulk series adapts for the MCU.
The Winter Guard
With Yelena and the Red Guardian both in the MCU, a Winter Guard series is definitely possible. The Russian superteam equivalent of the Avengers debuted in 1998 in Iron Man #9 from that year. Their comic book history goes back much further, as they were previously the Soviet Super-Soldiers who clashed frequently with the Avengers and Defenders.
Given the presence of so many Russian superheroes in the MCU now, they could be an intriguing team to explore either in the past or present of the franchise.
Daredevil
The Red Guardian's connection to Black Widow has the potential to bring him into contact with another major Marvel hero: Daredevil. While Natasha Romanoff's and Matt Murdock's strange comic romance wasn't explored in the MCU, their relationship could be reinterpreted with Yelena should there be a new Daredevil series or movie.
If Matt Murdock does appear in the MCU in the near future, then Yelena could take Natasha's place in the MCU Daredevil's life, with the Red Guardian looking over their shoulder.
Armor Wars
The Red Guardian didn't play a role in the original Armor Wars comic book storyline from the 1980s, but that could be different in the MCU series. Several Russian villains appeared in the comic, using stolen Stark technology. It's possible Red Guardian could fill this role on screen, especially if there is a question about where his shield came from.
Armor Wars will focus on War Machine as he likely deals with a storyline similar to the comics. That may lead him into a battle against the Red Guardian and other Russian characters like the Crimson Dynamo, who was namechecked in Black Widow.
Secret Invasion
Red Guardian is a potential character who could appear in Secret Invasion given the possible global scope of the show. Another link is through Yelena, whose connection to the Contessa - who played a role in the original comic book storyline - suggests Alexei could be in the series.
If the Skrull invasion of the Earth plays out the way it did in the major comic crossover, then it will be all hands on deck. The world will need every hero it can get, and the Red Guardian would be a good warrior to have on the front lines.
Captain America 4
A number of comic book storylines could provide the basis for the upcoming Captain America 4. While Captain America and Red Guardian have a rivalry in the comics primarily through the Avengers, no version of Red Guardian has a real connection to Sam Wilson.
The next movie could be a great opportunity for Alexei to try to add to his legend by taking on Sam in his new role as Captain America. Since Sam doesn't have superpowers, it probably would go a lot different than in the comic books.