Blackwatch is an antagonistic faction in the lore of the Overwatch franchise. It was the former covert operations arm of Overwatch.
Blackwatch was originally established after the Omnic Crisis. Before its disbandment it was led by Gabriel Reyes, one of the six founding members of Overwatch, and had several recruited criminals such as McCree of the Deadlock Gang and Genji of the Shimada Clan among its members. The purpose of Blackwatch was to perform more morally ambiguous operations that Overwatch could not do publicly, such as blackmail and assassinations. Because of this, Blackwatch's existence was kept in the dark from the public and even those who knew of it, such as Jack Morrison, kept it concealed.
However, feeling resentful that he had not been made a commander of Overwatch and that his work as a member of Blackwatch had been overlooked, Reyes revealed all of Blackwatch's crimes to the public, triggering the disbandment of both Blackwatch and Overwatch for its ties to the covert ops organization. Following Blackwatch's dissolution Reyes would go on to join the terrorist organization Talon along with fellow former Blackwatch member Moira. McCree would instead become a mercenary-for-hire, while Genji would rejoin Overwatch after it was brought back.