Black Ops (series)

Black Ops is a sub-series of the Call of Duty franchise from Activision, and includes Call of Duty: Black Ops and Call of Duty: Black Ops II, with Call of Duty: World at War being the backbone of the storyline while not an actual part of the sub-series. The games are made by Treyarch who also made Call of Duty 3.

Trivia
It is often considered a continuation of Call of Duty: World at War due to the presence of Viktor Reznov and Dimitri Petrenko in the game.