After being shown to CinemaCon attendees in April, the full "Doomsday" trailer is now public and brings together nearly every hero in the MCU.

"Doomsday" is the culmination of the MCU's multiverse-crossing storytelling over the past seven years and three Phases since "Avengers: Endgame" released and became the second highest-grossing movie of all time. The team-up film brings together almost every major character from across the MCU to face its latest villain: Doctor Doom, played by Robert Downey Jr. in his Marvel return.

The trailer shows the Marvel heroes assembling as Doctor Doom prepares to wreak multiverse-crossing war on the heroes. Thor faces off against Doom and also reunites with Chris Evans' Captain America, making his long-awaited return to the MCU after "Avengers: Endgame." Several of Fox's "X-Men" characters also officially cross over into the Avengers' universe, including Professor Xavier, Magneto, Mystique, Cyclops and Channing Tatum's Gambit from "Deadpool and Wolverine." After hitting the big screen last year, the Fantastic Four and Thunderbolts are also back to help the Avengers save the multiverse.

"Doomsday" hits theaters on Dec. 18, followed by "Avengers: Secret Wars" a year later. The Russo Brothers, after directing "Infinity War," "Endgame" and two "Captain America" movies, are back to helm both upcoming "Avengers" films.

After Iron Man sacrificed himself to defeat Thanos and save the world in "Endgame," Downey Jr. is back — but not as his original, iconic Marvel role. The details for his turn as Doctor Doom haven't been fully explained, but it's likely that Doom is a variant of Iron Man from another universe. He briefly appeared, though his face was hidden, in the post-credits scene of "Fantastic Four: First Steps."

The list of which Marvel stars are returning for "Doomsday" is long, and they were all showcased in a slow-burn stunt in March 2025 that revealed the cast members' names on the backs of chairs. Chris Hemsworth, Anthony Mackie, Danny Ramirez, Sebastian Stan, Paul Rudd, Tom Hiddleston, Letitia Wright, Winston Duke, Simu Liu and Tenoch Huerta are among the returning MCU characters for "Doomsday." The Fantastic Four and Thunderbolts, the two most recent teams added alongside the Avengers, will bring back Pedro Pascal, Vanessa Kirby, Joseph Quinn, Ebon Moss-Bachrach, Florence Pugh, David Harbour, Wyatt Russell, Hannah John-Kamen and Lewis Pullman.

Perhaps the most exciting castings for "Doomsday" are the past X-Men characters who are jumping into the MCU. They include Patrick Stewart, Ian McKellen, Kelsey Grammer, Alan Cumming, James Marsden, Channing Tatum and Rebecca Romijn.

To build hype for "Doomsday," Disney dropped four teaser previews tied to screenings of "Avatar: Fire and Ash" in late 2025 and early 2026. The first confirmed that Evans would return as Steve Rogers, aka Captain America, who now has a child; the second showed Hemsworth's Thor and his adopted daughter Love; the third gave the first look at Stewart's Prof. X, McKellen's Magneto and Marsden's Cyclops; and the fourth featured Wright's Black Panther, Huerta's Namor and Duke's M'Baku meeting Moss Bachrach's Thing in Wakanda.