Marvel has been coy about the title of Avengers: Endgame ever since Infinity War was released. However, months before we found out the official title for the climactic Marvel movie, film's directors Joe and Anthony Russo had hinted at it but no one really picked up on it.
Now, we know that Avengers: Endgame title is a reference to a line that Tony Stark (Robert Downey Jr) says in Avengers: Age of Ultron when he tells the rest of the Avengers that the galaxy beyond Earth is the "endgame".
And of course, everyone remembers the line from Doctor Strange (Benedict Cumberbatch) in Infinity War where he tells Tony, "We're in the endgame now," before turning to dust.
Now, one Reddit user noticed that this might be a clue for Tony Stark to figure out how to stop Thanos.
Strange saw that Tony was going to have to go back in time, but he had to give him a hint as to when to go to. He couldn't outright just tell him without breaking a time continuum (or just a time travel movie rule).
Ultron will be a key to stopping Thanos. Ultron had just come out and escaped into the world. He was meant to be the key to stopping the Endgame in Tony's mind. Tony might go back in time and fix Ultron when the party is going. When Ultron was created Tony even said to Bruce in disbelief "Were we even close to an interface?" He could have already gone back in time and was a catalyst to creating Ultron. Or someone else did and Tony will stop them.
It's believed that time travel and flashbacks will play a huge role in Avengers: Endgame, which releases in theatres on April 24.