He is the overall secondary antagonist of The Dark Army series.
For more info on Deathshead prior to the events of The Dark Army, go here.
Weeks after the failure at Isenstadt, Deathshead has hidden himself in a secret base in the German mountains, and is assisted by brothers, Wilhelm and Karl Von Starke. He later sends infantry troops to a nearby village for excavational plans.
Not much is known about Deathshead in Downfall, but based on what the creator said, Deathshead forces B.J. to fight with him against his former assistant, Karl.
Deathshead's story continues in Wolfenstein: The New Order.