Cassidy had already made a name for himself as a member of the notorious Deadlock Rebels Gang, when he and his associates were busted in an Overwatch sting operation. With his expert marksmanship and resourcefulness, he was given the choice between rotting in a maximum-security lockup and joining Blackwatch, Overwatch's covert ops division. He chose the latter.

Although he was initially cynical, he came to believe that he could make amends for his past sins by righting the injustices of the world. Cassidy appreciated the flexibility afforded to the clandestine Blackwatch, unhindered by bureaucracy and red tape. But as Overwatch's influence waned, rogue elements within Blackwatch sought to bring down the organization and turn it to their own ends. After the destruction of Overwatch's Swiss HQ, Cassidy wanted no part of the infighting. He set off alone and went underground.

He resurfaced several years later as a gunslinger for hire, fighting for causes he believed were just. But trouble has a way of finding old outlaws, and Cassidy’s list of enemies is long. He fought Talon while aboard a hypertrain in Texas and busted a heist by his former Deadlock Rebel allies in New Mexico. During the latter incursion, he freed Echo, the life’s work of his late friend, Dr. Mina Liao.

After Cassidy received the call to rejoin Overwatch, a nostalgic run-in with Ana Amari had the gunslinger contemplating his future. Presented with growing security threats around the world and the possibilities afforded by a new team, Cassidy went on a mission to recruit heroes forged from various incursions around the globe. Reinforced with fresh faces, Cassidy and his new recruits are out in full force to strengthen Overwatch's presence worldwide.