[1] He led the design and content creation teams of the original Guild Wars.
[2] Before co-founding ArenaNet, he worked as a company director and a lead programmer at Blizzard Entertainment where he developed the 3D rendering engine of Warcraft III: Reign of Chaos and led the development of Battle.net.
O'Brien also previously developed an Apple II emulator for Windows, AppleWin, and old DOS ASCII game, Pyro 2.
In early October 2019, through the official Guild Wars 2 news page, O'Brien announced his departure from ArenaNet and his intention to start a new development studio.
This biographical article relating to a video game specialist is a stub.