With even the title being kept under the tightest of wraps, it’s honestly anyone’s guess as to what could happen next in Avengers 4. Even prior knowledge of the comics can only take one so far at this point.
But thanks to certain events in Infinity War and other recent Marvel movies, casting rumors, name drops, and even some of the aforementioned comic knowledge we managed to pick out a few characters we may very well see in next years movie.
A’lars of Titan
Little, if any, information has been given about Thanos’s homeworld and people aside from their self-destructive ways. One, in particular, was namedropped during Infinity War, however: A’lars, his father. In the comics, A’lars, or Mentor, was the sole survivor of Thanos’s destruction of the Eternal colony on Titan and often allied with cosmic heroes against his bloodthirsty son.
In the film, there is no indication of any survivors on Titan after resource drain leads to both a mass extinction event and Thanos’s motivation for wiping out half the galaxy. But it’s still not out of the realm of possibility that one could appear, especially with Iron Man currently stuck on the planet. Even if he didn’t survive, A’lars and possibly other members of his family could still appear in either flashbacks (perhaps setting up the rumored Eternals movie) or as a Soul World manifestation like the one of young Gamora.
Multiple directors and Marvel execs have adamantly denied the presence of Adam Warlock in the MCU for years. Guardians of the Galaxy director James Gunn allowed us a hint of the character in a post-credits scene showing Adam’s gestation in a Sovereign cocoon, he’s shied away from confirming it as anything other than a random cameo similar to the first film’s Howard the Duck and Cosmo the Space Dog’s appearances. Still, it beggars belief that the cosmic character won’t have any presence whatsoever in a movie concerning not only Thanos and the Infinity Gauntlet but the Soul World of the Soul Gem, and many fans hope for at least another after-credits scene.
(Teen) Cassie Lang
One particularly persistent casting rumor pertains to Ant-Man’s young daughter Cassie Lang and seems to indicate the already established character being aged up to a teenager. This is interesting for several reasons; aging Cassie up from a child indicates that there will either be an extremely long gap between Infinity War and Avengers 4 or the implementation of time travel (probably with the Time Stone). Additionally, in the comics the teenage Cassie is a hero herself, using Pym Particles to grow or shrink like her father. Cassie as a teenager could very well be a big step towards the next phase of the MCU and new generation of heroes.
A Celestial in Guardians of the Galaxy (2014)
In the comics, the Celestials are essentially the oldest living beings in the universe and nearly single-handedly responsible for the natural diversity of the evolutionary process. They more directly had a hand in creating the Eternals, a godlike race that includes Thanos and A’lars. While in the movies these beings seem to be either extinct or far from the occupied centers of the galaxy, the combined events of the last GOTG movie (where one of their number, Ego, was killed) and Infinity War could be enough to bring them into the scene. Perhaps they could even be the key to stopping the mad Titan or prove to be an even bigger threat once in possession of the Stones once more.