Warning: SPOILERS for Thor: Ragnarok ahead!
Matt Damon has so much star power in Hollywood that he could certainly lead his own superhero movie. Instead, the actor debuted in the Marvel Cinematic Universe last month during Thor: Ragnarok not as one of the leads, but as someone playing one of the main characters, Upon returning to Asgard, Thor saw a play about Thor's previous adventures in the modern day MCU, and Damon's Asgardian character was performing the Loki role. It was an amusing cameo, and Damon has revealed that his involvement originated from simple phone calls from Thor himself, Chris Hemsworth, and director Taika Waititi. Damon recalled:
Chris just called me up, and Taika called me up, and I'm friends with those guys. They pitched me the idea and I just thought it was hysterical, the idea of basically an intergalactic community theater actor kind of living out Tom Hiddleston's character's fantasy. I just thought it was just a great, funny bit, and very easy to do. Those guys were a lot of fun, and Taika runs a really fun set. It was a light lift for me.
As Matt Damon informed Collider, he didn't have any aspirations to join the MCU before Thor: Ragnarok, but when Chris Hemsworth and Taika Waititi called him, he saw it as opportunity to do something easy and fun for one of the most popular movie franchises. Along with Damon playing the Loki actor, Thor: Ragnarok's "stellar" stage production also featured Sam Neill (who Waititi previously worked with on Hunt for the Wilderpeople) as the Odin actor and Luke Hemsworth as the Thor actor. Of course, now there's the question of if any of those three actors exist within the MCU, and if they do, what would they think about there being Ashardians who look just like them.
At the end of Thor: The Dark World, Loki banished Odin to Earth and disguised himself as the All-Father so that he could rule Asgard. Because Thor was so busy with his Avengers duties and trying to solve the mystery of who was gathering the Infinity Stones together, the God of Thunder wasn't spending that much time in his home realm, and thus didn't learn what his deceptive brother had done until several years later in Thor: Ragnarok. But upon defeating Surtur, returning to Asgard with the fire demon's crown, coming across this play that made Loki out to be more of a hero then he actually was (something tells me it won't be winning any Asgardian Tonys) and seeing how strange "Odin" was acting, he finally realized what Loki had done and forced him to reveal himself to the Asgardian population. Cut to the end of the movie, Asgard was destroyed, but Thor and his allies successfully evacuated its citizens, so one can only hope that Matt Damon's character and his fellow performers made it out alive as well.
Thor: Ragnarok is wrapping up its theatrical run, but you can expect it to be available on home media in the coming months. Both Thor and Loki will be back for Avengers: Infinity War on May 4, 2018.