Which team-based shooter inspired part of Overwatch's development?

Team Fortress 2 was the team-based shooter that inspired part of Overwatch’s development.

Blizzard’s developers studied the large-scale, fast-paced teamplay of Team Fortress 2 while shaping Overwatch’s own formula. They combined those ideas with the smaller-scale cooperation and character-focused structure associated with multiplayer online battle arenas, producing a shooter built around heroes with different abilities.

The influence does not mean Overwatch is a direct sequel or a copy. Team Fortress 2 helped demonstrate how class-based roles, readable character silhouettes, and coordinated objectives could work in a colorful multiplayer shooter. Overwatch then added its own cast, setting, ability systems, and emphasis on switching heroes during a match.

Overwatch’s development began after the cancellation of Blizzard’s Titan project. The remaining team used some Titan assets and concepts to prototype a new game, eventually announcing Overwatch at BlizzCon in 2014.