Robert Downey Jr. is back as the villain in the first Avengers: Doomsday trailer

Marvel has released the first full trailer for Avengers: Doomsday, confirming a December 18, 2026 release date after an earlier delay from May. The footage is the clearest look yet at Robert Downey Jr.'s return to the MCU — not as Tony Stark, but as the armored supervillain Doctor Doom. After years of franchise fatigue and uneven box-office results, this is Marvel's biggest swing in years.

The pitch

Downey's casting as Doom was announced at San Diego Comic-Con in July 2024 and was reportedly his own condition for coming back: the Russo Brothers — Anthony and Joe, who directed both Infinity War and Endgame — had to return alongside him, and they're also locked in for the follow-up, Secret Wars (2027). The directors are framing the project as a "complete reinvention" and a "phase zero" reset for the MCU.

The trailer backs up the scale of that claim. It features an enormous ensemble: the Fantastic Four, the X-Men in their current MCU form, Chris Evans back as the original Steve Rogers Captain America, Shang-Chi, Thor, and characters from Wakanda — characters drawn from at least three converging storylines. That's 39 films of continuity the Russos are working with, which makes "starting over" a complicated pitch. According to Wikipedia (Avengers: Doomsday), Downey cited the physical expressiveness of Doom's masked role as part of his motivation — a full-face helmet means the performance lives in posture and eye work.

The stakes

Marvel's recent track record has been inconsistent. Several MCU entries underperformed at the box office between 2022 and 2025, and the original plan to build the next saga around Kang the Conqueror collapsed after actor Jonathan Majors was dropped following a legal conviction. Doom — and Downey — are the direct replacement. Rotten Tomatoes notes that Variety's tracking as of early 2026 already placed Doomsday as a strong performer, potentially the highest-grossing film of the year.

The casting has drawn some criticism — notably that leaning on Downey is a safe legacy play rather than a genuine creative risk, and that Doctor Doom, a character with Romani heritage in the comics, could have gone to a different actor. Those debates aside, the trailer delivers exactly what the MCU built its audience on: a recognizable face in an unexpected role, a lot of heroes in one frame, and a release date to circle on the calendar.

Avengers: Doomsday opens December 18, 2026.