William J. Blazkowicz (Sergeant 1st Class) was a UAC Marine stationed on Phobos Compound. His decapitated body is discovered in a storage room on the base by Joan Dark and her team. She calls him 'one of our own'. Her commander thinks of Sergeant Blazkowicz's family.
Her group finds a blue keycard on his corpse, which opens the door to the BFG 9000 armory. She thanked Sargeant Blazkowicz for giving her access to the cabinet.
Behind the scenes
This is a homage to the character of William J. Blazkowicz from the Wolfenstein series, and the original Doom Marine B.J. Blazkowicz (Doom) (& Stan Blazkowicz) of the Doom/Doom RPG series, his descendants. Some reviewers have noted that Doomguy also "dies" at the end of Knee Deep in the Dead during the initial Phobos invasion, which this may also be a nod to (though in the games he somehow arises again to continue his fight in Deimos, and the bowels of hell where the moon has been transferred to).