William "B.J." Blazkowicz is the protagonist in most of the Wolfenstein series. He first appears in 1992, in Wolfenstein 3D.
Blazkowicz was born in the United States to a family of Polish immigrants. There are hints that one of his parents is Jewish, though Bethesda Softworks never explicitly stated that and the developer MachineGames decided to leave it up to the player to interpret the events and dialogs in the games.
During WW-II, Blazkowicz started as a sergeant in the U.S. Army Rangers. He's later promoted to an officer's commission and recruited as a secret agent for the United States Office of Secret Actions (OSA), a fictional version of the OSS.
The (partially retconned) timeline for this character would be Wolfenstein 3D, Spear of Destiny, Return to Castle Wolfenstein, Wolfenstein (2009), Wolfenstein: The Old Blood and Wolfenstein: The New Order.