“We lost friends. We lost family. We lost a part of ourselves.” These are the words spoken by the beacon of light, Captain America (Chris Evans), as he attempts to rally the troops in the wake of Thanos’ successful snap. The fact that Joe and Anthony Russo lay those words over the first images of Hawkeye suggest that one surviving Avenger lost a lot in the snap, and it changed him.
Hawkeye (Jeremy Renner) will be Ronin in Avengers: Endgame, and he looks sick.
Ronin, in the comics, is a secret identity used by numerous characters, with Clint Barton being the second official person to adopt the moniker. It’s largely used for a lone warrior, someone who is fighting as a samurai, and who needs to protect their identity because they plan to push the envelope. Comic creator Brian Michael Bendis initially planned for Daredevil to assume the mantle of Ronin, but plans shifted, and Hawkeye wore the costume in the aftermath of Civil War.