Cate Shortland, director of Natasha Romanoff's history and what she was up to between the events of Captain America: Civil War and Avengers: Infinity War. Black Widow also goes back to Natasha's childhood, spent in Ohio with Melina Vostokoff and Alexei Shostakov AKA Red Guardian, who act as pseudo parents to her and Florence Pugh's Yelena Belova. When Natasha discovers that Dreykov is still operating the Red Room, she enlists Yelena to help her break Alexei out of prison in the hopes of taking Dreykov down once and for all.
Of all the new characters introduced in Black Widow, Red Guardian is one of the standouts. Harbour's character is obsessed with himself and his time as Russia's answer to Captain America all while avoiding the guilt he feels about sending Yelena and Natasha into the Red Room. Alexei also seems to want to rekindle his relationship with Rachel Weisz's Melina as he grapples with his past actions and how his family feels about it in the present.
In an interview with The Wrap, Shortland says that she filmed plenty of material with Red Guardian and his family, footage that often left her crying with laughter. The director goes on to say that there was plenty of stuff that didn't end up in the movie and this is why she ultimately thinks Red Guardian needs his own film, one that would be extremely funny.
Sometimes — not sometimes — often I would be crying with laughter. And there was so much good stuff that didn’t end up in the film. But I think that’s why Red Guardian needs his own movie. Because it will be so funny.
With Red Guardian left alive at the end of Black Widow, it's more than possible that he could get his own solo movie in the future or even a Disney+ series. Harbour has even speculated as to what Red Guardian was up to during Infinity War and Endgame, meaning he has thought extensively about what his character's future looks like. It's clear that the actor invested a lot in this character, from the emotional core of Alexei to the more outwardly boastful traits that he uses to deflect from these feelings.
Interestingly, Harbour has had discussions about Red Guardian's MCU future, but he wasn't able to reveal anything. If a Red Guardian solo movie were to happen, it seems like it may not be for quite some time. With the MCU moving full steam ahead into Phase 4 of the franchise, the plans are still starting to take shape in the eyes of the audience. Black Widow gave a hint as to where Yelena would end up after the film, but as for the rest of the characters, it remains to be seen where they could appear again.
Source: The Wrap