The Guardians of the Galaxy and Thanos
We can't say for certain whether digitally-created characters will be a part of the film, but considering that we do know that fellow Guardians Nebula, Gamora and Drax are all set to return, we can probably safely assume Rocket Raccoon and Groot will also be involved. Zoe Saldana and Karen Gillan have both been seen in set videos of Avengers 4 in their respective make-up and costumes, and Drax actor Dave Batista has gone on record to say that he is hitting the gym harder than ever before for his short stint on the upcoming movie, a goal he's aiming to achieve if only to match the dwarfing presence of Thanos actor Josh Brolin. This statement, along with Brolin's previous interviews, also confirm that Thanos will very much be involved in the film. The Guardians' fearless leader Star-Lord, an iconic presence in the MCU thanks to Chris Pratt's iconic performance, is also expected to return to Atlanta for filming.
Ant-Man and the Wasp
Paul Rudd's Scott Lang has been confirmed to be in Infinity War for some time, with set photos teasing his involvement in the film -- but, alas, nothing was announced about his partner in superhero crime, Evangeline Lily's Hope Van Dyne, aka the Wasp. However, all of that is about the change come Avengers 4. In fact, the duo's very own team-up movie, Ant-Man And The Wasp, is set for release on July 6th, 2018, a mere two months after the release of the third Avengers movie. The Ant-Man sequel is set to fully establish Hope as the Wasp, which will cement her place among the MCU roster of superheroes. Both actors have been seen in a set video of Avengers 4, giving us an early look at their amazing new costumes.
Hawkeye and Black Widow
Hawkeye has always been a bit of a mysterious character. He kept his family secret from all of his friends, he retired from the Avengers life for five minutes until the Civil War brought him back to the fold and he's now currently on the run from the government. And after his appearance in Infinity War, we already know that Renner is returning for its sequel, with a brand new, and quite mysterious, haircut to go along with it.
Scarlett Johansson's Black Widow is in a similar situation to her old S.H.I.E.L.D. partner. Last we saw her, she was also on the run from the government, after "defecting" from Tony Stark's side of the Civil War argument. We've already seen her new blonde hair for Infinity War, and now we know that the character will be in Avengers 4, as the actress has been spotted filming the movie in Tokyo. It just so happens that there are reports claiming that Jeremy Renner is also involved in the Japan-based scenes.