Overwatch (retroactively referred to as Overwatch 1) was a 2016 multiplayer first-person shooter video game by Blizzard Entertainment. The game was first released for PlayStation 4, Windows, and Xbox One in May 2016 and Nintendo Switch in October 2019, with cross-platform play supported across all platforms. Described as a "hero shooter", Overwatch assigned players into two teams of six, with each player selecting from a large roster of characters, known as "heroes", with unique abilities. Teams worked to complete map-specific objectives within a limited period of time. Blizzard added new characters, maps, and game modes post-release, all free of charge, with the only additional cost to players being optional loot boxes to purchase cosmetic items.

Overwatch was Blizzard's fourth major franchise and came about following the 2014 cancellation of a massively multiplayer online role-playing game, Titan. A portion of the Titan team were inspired by the success of team-based first-person shooters like Team Fortress 2 and the popularity of multiplayer online battle arena games, and would go on to create a hero-based shooter which emphasized teamwork. Some elements of Overwatch borrowed concepts from the canceled Titan project. Overwatch was unveiled at the 2014 BlizzCon event and was in a closed beta from late 2015 through early 2016. An open beta before release drew in nearly 10 million players.

Overwatch received universal acclaim from critics, who praised the game for its accessibility, the diverse appeal of its hero characters, its cartoonish art style, and enjoyable gameplay. Blizzard reported over US$1 billion in revenue during the first year of its release and had more than 50 million players after three years. During its lifetime, Overwatch was considered to be among the greatest video games of all time, receiving numerous game of the year awards and other accolades. The game was a popular esport, with Blizzard funding and producing the global Overwatch League. On October 3, 2022, the Overwatch servers were shut down and the game was made unplayable, and its sequel, Overwatch 2, was released in a beta state the next day.

Overwatch was an online team-based game generally played as a first-person shooter. The game featured several different game modes, principally designed around squad-based combat with two opposing teams of six players each. Players selected one of over two dozen pre-made hero characters from one of three class types: Damage heroes that deal most of the damage to attack or defend control points, Tank heroes that can absorb a large amount of damage, and Support heroes that provide healing or other buffs for their teammates. Each hero had a unique skill kit, defining their intrinsic attributes like health points and running speed, their primary attacks, several active and passive skills, and an ultimate ability that can only be used after it has been charged through dealing damage to enemies and healing allies. Players could change their hero during the course of a match, as a goal of Overwatch's design was to encourage dynamic team compositions that adapt to the situation. The game's genre has been described by some journalists as a "hero shooter", due to its design around specific heroes and classes.

The game featured game modes for casual play, competitive ranked play, and for supporting esports competitions including Blizzard's Overwatch League. These modes were generally centered around sequentially securing control of points on the map, or escorting a payload between points on the map, with one team attacking while the other defends. Other modes set aside for casual matches include solo and team deathmatch, capture-the-flag, and unique modes run during various seasonal events. More recent updates had enabled users to craft their own game modes with a limited set of scripting tools. Regardless of winning or losing a match, players gained experience towards a player level, and on gaining a new level, received loot boxes that contain cosmetic items that they can use to customize the appearance of the hero characters but otherwise does not affect gameplay. Loot boxes could also be purchased through microtransactions.

The backstory to Overwatch is described through animated shorts and other information distributed by Blizzard in promoting the game.

Overwatch was set sixty years into the future of a fictionalized Earth, thirty years after the resolution of what is known as the "Omnic Crisis." Before the Omnic Crisis, humanity had been in a golden age of prosperity and technology development. Humans developed robots with artificial intelligence called "omnics", which were put to use to achieve economic equality, and began to be treated as people in their own right. The Omnic Crisis began when the worldwide automated "omnium" facilities that produced them started producing a series of lethal, hostile robots that attacked humankind. After individual nations' efforts failed to ward off the omnics, the United Nations quickly formed Overwatch, an international task force designed to combat this threat and restore order.

Two veteran soldiers from the Soldier Enhancement Program were put in charge of Overwatch: Gabriel Reyes and Jack Morrison. Though Overwatch successfully quelled the robotic uprising and brought many talented individuals to the forefront, a rift developed between Reyes and Morrison due to Reyes being the official leader of the group despite everyone viewing the more popular Morrison as their true leader. Eventually, Morrison was made the leader of Overwatch while Reyes was given charge of Blackwatch, Overwatch's covert operations division, fighting terrorist organizations like Talon, a group that appears to be trying to start a second Omnic Crisis, and Null Sector, a group of Omnics that revolted against the society that persecuted Omnics following the first Crisis. Overwatch continued to maintain peace across the world for several decades in what came to be called the "Overwatch Generation" as the team gained more members, but the rift between Morrison and Reyes intensified. One night, Blackwatch was dispatched to arrest a notorious mobster with ties to Talon. After infiltrating the compound, Reyes chose to execute the mobster rather than let him buy his way out of prison. This action caused Blackwatch and their less heroic actions to be exposed to the public. Several allegations of wrongdoing and failures were leveled at Overwatch, leading to a public outcry against the organization and in-fighting between its members, prompting the UN to investigate the situation. During this, an explosion destroyed Overwatch's headquarters in Switzerland, purportedly killing Morrison and Reyes among others. The UN passed the Petras Act, which dismantled Overwatch and forbade any Overwatch-type activity.