Clint Barton/Hawkeye

Hawkeye (Clint Barton) is a shield agent and a member of The Avengers. He is codenamed Hawkeye. He was an orphan who became a master archer while in the circus.

Eventually, in his adulthood, he became an Agent for SHIELD.

Thor
Clinton Barton was serving in a military branch of S.H.I.E.L.D. when freakish atmospheric events, followed by the discovery of an immovable hammer in an impact crater, saw him deployed to New Mexico as part of a security force to protect the object. Soon after his deployment, an intruder broke into the S.H.I.E.L.D. compound and fought his way to the mysterious hammer. Barton responded to the alarms by collecting a compound bow and claiming a high vantage point suspended from a crane. Despite making several radio transmissions warning that the intruder was reaching the hammer, Barton was never given a shoot order, forcing him to let his target go.

The Avengers
His mission complete in New Mexico, Barton was then assigned to guard the Tesseract at a S.H.I.E.L.D. research facility. When it began emitting increased levels of gamma radiation the entire facility was placed on high alert and most staff were evacuated, while Barton and a few others remained as rearguard for as long as they could. The emissions proved to be a precursor to the unexpected appearance of Loki Laufeyson, who had used it to reach Earth extradimensionally. Barton and the other guards were quickly overpowered and Barton was promptly enslaved into Loki's service.

For a time, Barton served Loki as a guard, enforcer, and assassin, completely without volition. When Loki was incarcerated in the S.H.I.E.L.D. Helicarrier, Barton led a commando raid against the vessel to extricate him, as well as to directly add to the chaos that Loki was seeding within his enemies. The attack drew him into direct conflict with Black Widow, his staunchest ally, who both bested him in close quarters and scored a blow to his head that helped to dislodge Loki's hold over him.

Upon recovering from the ordeal, Barton vowed to put Loki down, going so far as to propose an arrow to the Asgardian's eye socket. To that end he willingly grabbed his equipment and offered to pilot Captain America and Black Widow to Loki's location, which had been determined as New York City. Once there, the trio formed up with Thor Odinson, Dr. Bruce Banner (the Hulk), and Tony Stark (Iron Man), to fight Loki together. The group quickly found themselves embroiled in a battle for New York City against a huge invasion force of Chitauri that Loki had summoned using the Tesseract. Barton, now operating under the pseudonym of "Hawkeye" initially fought the alien warriors on the streets before switching to a higher vantage point atop a high-rise building to snipe at the alien air support. At one point he even took a shot at Loki, and although the aim was true, Loki simply snatched the arrow from the air before it struck. Hawkeye had planned in advance however, and had rigged the arrow with an explosive head that knocked Loki's transport out of the sky.

When the battle was over Hawkeye and the others parted company. He and Agent Romanoff returned to the service of S.H.I.E.L.D. until the next time the world would call on the Avengers.