"Thor: Ragnarok" will play a crucial role in setting up the back half of Marvel's Phase 3, and that may mean some important characters have to die.

"Ragnarok is the end of all things. What are we supposed to do, let people life?!" screenwriter Christopher Yost tweeted on Nov. 5. Yost will write the script for the next "Thor" installment after working on the first sequel, "Thor: The Dark World."

The titular character, played by Chris Hemsworth, may not even be spared depending on how closely Yost chooses to adapt his screenplay from the "Ragnarok" comic book in which Thor dies. His death comes among others during a massive battle between the Nine Realms that Loki, who currently sits on the Asgard throne, may have a hand in starting.

"This is a very important movie for us in Phase 3" Marvel Studios President Kevin Feige said at the Marvel event announcing the Marvel Phase 3 movie slate on Oct. 28. He also confirmed Tom Hiddleston will reprise his role as Loki in the film. "We plan on taking Thor to another level. It picks up where we leave Thor in 'Avengers: Age of Ultron' and impacts everything that comes after."

Idris Elba recently confirmed his character Heimdall and Loki will also appear in a scene with Thor in the "Avengers" sequel. The scene may set up "Thor 3," which will start in the immediate aftermath of "Age of Ultron," according to Feige.

Three films will premiere between "Avengers: Age of Ultron" and "Thor: Ragnarok" including "Captain America: Civil War," "Doctor Strange" and "Guardians of the Galaxy 2."

"Avengers: Age of Ultron" will open on May 1, 2015 and "Thor: Ragnarok" is scheduled to open on July 28, 2017.