Captain America has battled many enemies over the years, but arguably the greatest of them all is Johann Schmidt, a.k.a. The Red Skull. Marvel's star-spangled hero squared off against the scarlet-visaged evildoer in 2011's Captain America: The First Avenger, but like most of the Marvel Cinematic Universe's villains, Red Skull only showed up for one movie. It's generally been assumed that he died upon touching the Tesseract, a.k.a. the Space Stone, but some have speculated that he's still alive, and a new comic book hints that the former HYDRA head may have been transported to another corner of the MCU.
In case you need a refresher on Captain America: The First Avenger, Captain America and Red Skull had their last battle aboard the plane carrying HYDRA's weapons of mass destruction, and during the fight, the container carrying the Tesseract was damaged. Panicking, Red Skull grabbed the Tesseract, which resulted in the flesh on his hand burning away, followed by a portal opening up that he then disappeared through. While it seemed as though Red Skull was simply disintegrated due to making direct contact with the Tesseract, Marvel's Avengers: Infinity War Prelude #2 (via Screen Rant) suggests that wasn't the case. During the comic book issue, Wong goes over the history of the Infinity Stones with Doctor Strange, and during the portion on the Space Stone, we see a flashback to Red Skull's last appearance. This time, however, the scene is illustrated to make it look like Red Skull was transported somewhere else in the universe.
Assuming that Red Skull did indeed survive his contact with the Tesseract (and given how powerful and sometimes unstable the Infinity Stones can be, there's no guarantee of that), that means that Red Skull was likely transported to another planet. Given his obsession with mythology and legends, the villain would undoubtedly be pleased to learn that life existing elsewhere in the galaxy, though that would be to the detriment of those around him. Of course, this event happened more than 70 years ago, so Red Skull would have needed to find a way to halt or slow down his aging, otherwise he'd be long dead in the present day, no matter where he's located.
So where does that leave us? Well, so far there's been no indication that Marvel is planning on bringing back Red Skull, though with Avengers: Infinity War a few months away and Avengers 4 capping off Phase 3 next year, perhaps Red Skull's return is one of the surprises in store. With Chris Evans' MCU future uncertain post-Avengers 4, it would be great if Steve Rogers could have one last confrontation with his arch-nemesis. While Hugo Weaving enjoyed his time playing the Red Skull, that doesn't necessarily mean he would reprise the role, be it due to scheduling issues or simply not being interested in revisiting the character. Of course, given Red Skull's history of body-switching in the comics, it wouldn't be unprecedented to find a new actor to take over as the antagonist.