A good chunk of Doomsday could focus on a clash between Avengers and X-Men with RDJ’s Doom cackling in the background, with a kidnapped Franklin by his side. The premise certainly gives the Fantastic Four a reason to breach their multiversal walls and zip over to 616 to meet the New Avengers.

But that all changes in the movie's post-credits scene, when the vibe shifts and suddenly there's a metal-masked stranger hanging out in the living room of the Baxter Building. If you've seen The Fantastic Four: First Steps and need some Reed Richards–level tutoring to figure out just what the heck is going on,

Here's who that mysterious figure was in the credits scene of "The Fantastic Four: First Steps" and how it sets up Doomsday.