8. They might want to have a word with John Carmack about that...
Games Workshop claims to have trademark on it as they've used the term since 1995.
Doom was released in late 1993. In that game (the first in what became one of the most popular video game franchises in history), you played as Buddy Dacote (yes, the dude had a name), a Space Marine in the United Nations Space Marine Corps.
Plenty of other prior art is cited here, but even if you limit "prior art" to the electronic world, which appears to be what Games Workshop is doing, they still can't win. Id Software's creation predates their use of the term by more than a full year.