Warning: MAJOR SPOILERS ahead for Avengers: Endgame
Hawkeye may have been entirely absent from Avengers: Infinity War, but he makes up for it in Avengers: Endgame by finally getting the kind of story arc that fans have been waiting for - and makes a strong case for getting a bigger role in Phase 4. Endgame opens with Clint, enjoying his (ankle monitor-enforced) time off from the superhero gig by teaching his daughter, Lila, how to use a bow and arrow and spending quality time with his family. That quality time comes to an abrupt end, however, when Lila turns to dust, followed shortly by Clint's wife, Laura, and his two sons.
We first met Jeremy Renner's Clint Barton in Thor, where he was working with Phil Coulson for S.H.I.E.L.D. and kept an eye on Thor's attempt to reclaim Mjolnir from above. It was a brief appearance, but set Hawkeye up for his return in The Avengers. On a team that includes a Norse god and a giant green rage monster, Hawkeye was largely relegated to a support role, spending part of the movie under the thrall of Loki and, when he was freed, spending most of his time in the Battle of New York picking off random Chitauri soldiers and keeping an eye on the battle from above in order to give the other Avengers advice.
In Avengers: Age of Ultron we got the major reveal that Clint Barton has somehow been maintaining a secret life as a family man alongside his S.H.I.E.L.D. and Avengers commitments. Director Joss Whedon fought hard to keep the sequence at Hawkeye's farm in the movie, but while it certainly added a layer to the character, he still spent most of the movie on the sidelines - his main arc being a friendly rivalry with Quicksilver that ended in Quicksilver sacrificing himself to save Hawkeye and a little Sokovian boy.
Hawkeye's role in Captain America: Civil War was typical of the character's appearances by that point. He was once again on the margins, but he also once again got his own standout moment - in this case, his angry and mocking greeting to Tony "The Futurist" Stark after he and the other superheroes on Captain America's side of the war are imprisoned in The Raft. Renner is excellent in the role of Clint Barton, and always makes the most of whatever screen time he has, but since he's not one of the Avengers that has their own solo movie franchise, he's always been left on the sidelines while Captain America, Thor, and Iron Man take center stage.
In Avengers: Endgame (perhaps to make up for not appearing in the previous movie at all), Hawkeye finally got a chance to really shine. We get to see the tragic loss of his family that triggers his transformation into Ronin. We get to see him five years later, living a lonely life as a vigilante assassin. It's Hawkeye who first tests Tony's time travel device, going back in time for a brief and painful brush with his lost family. Ultimately, it's Hawkeye who constantly reminds us of what's at stake; other characters have lost friends and loved ones, but Hawkeye saw his entire life disappear when Thanos snapped his fingers. If the Avengers fail in their mission, he will never see his wife and children again.
The mission to get his family back ends up costing Hawkeye dearly. He and Black Widow get some quiet away from the noise when they travel to Vormir to retrieve the Soul Stone, realizing only too late that one of them will have to die in order to complete the mission. Hawkeye doesn't hesitate when it comes to sacrificing himself, fighting Black Widow for the "privilege" of dying, and during this struggle it becomes clear that he's afraid the past five years have changed him too much for him to ever return to his family. He ultimately succeeds in his mission, but at the cost of his best friend.
Now that Tony has died, Captain America has passed the torch (well, shield) to Sam, and Thor has left Valkyrie in charge of Asgard so he can join the Guardians of the Galaxy, there's room for Hawkeye to take center stage. A Black Widow movie is already being planned for Phase 4 of the MCU, which has a good chance of featuring Hawkeye in at least a cameo role. At the risk of diminishing Natasha's role in her own movie, the two characters are so closely intertwined that it would almost be a shame if their relationship wasn't further explored in Black Widow.
Renner initially signed a five-film deal with Marvel Studios that came to an end with Endgame, but he's set to return in a Disney+ TV show, in which he will train up Kate Bishop as a new Hawkeye. Beyond that, however, Hawkeye's role in Avengers: Endgame made a strong case for the character getting his own solo movie in Phase 4 (perhaps with Kate Bishop along for the ride). He's well-suited to an espionage thriller like Captain America: The Winter Soldier, and his weapon of choice could make for some truly dynamic and exciting action sequences.
