It's pretty funny, Warcraft and Starcraft are both blatant ripoffs of GW's Warhammer and WH40k. I even recall reading somewhere the original Warcraft RTS was to be an officially licensed Warhammer game. But gee whiz, I wonder why we don't see legal action brought against Blizzard?

Starcraft rips off both WH40k and Aliens, but I think it rips of Aliens more. Plus, Aliens was released 1 year before WH40k, so it has precedence. And Aliens ripped off Starship Troopers (the book), and Starship Troopers (the movie) rips off Aliens. It's complicated.

WH original and Warcaft are both simpler - they both rip off LOTR.

Which, in terms of trademark, is very irrelevant :).

This is a weak trademark, it has no secondary meaning that I can discern. You have marines. They're in space. Thus, "space marines." That would seem to fall under the weaker classes of trademark protection[1] and even though I have long known about Warhammer 40K, the words "space marines" do not make me (or most other people I know) think of Warhammer 40K. Personally, that term makes me think of the Aliens movie and Starcraft. They're nowhere near as famous.

Of course, the problem here is that they have more lawyers and wherewithal to contest this than most. Your average person does not have the resources to make a federal case out of this and their lawyers have a perverse incentive to be assholes when trying to prop up a weak trademark claim.

[1] http://www.bitlaw.com/trademark/degrees.html

This is all true and the interesting part of the story. My point is that just crying "prior art" doesn't work in trademark. Observations like yours do.

So, putting "Space Marine" in a title might a bad idea, but having marines in space (with or without mechanized body suits) should be fine. To reduce legal risks, you might want to call them "Space Core Maines" or "Space Marine Core".

And blizzard (nor anyone else) should have to license the term from GW. According to wikipedia:

The earliest known use of the term "space marine" was by Bob Olsen in his short story "Captain Brink of the Space Marines" (Amazing Stories, Volume 7, Number 8, November 1932)

There is no need for lack of prior art in trademark law, as multiple people have stated in this thread.

Blizzard was obviously "parodying" the Colonial Marines from Aliens. If you click on them enough, they'll even quote Aliens (as will the Dropship). A little bit of comedy makes almost everything legal (in the US).

Early Blizzard employees have given at least one interview where they said that Warcraft and Starcraft were inspired by their love of the Warhammer and Warhammer 40k universes.

I may be wrong but I think that the Starcraft unit is always called 'Marine' and not 'Space Marine'

I actually thought the same and it seems to be true in the english version, but for example not in the german one:

http://eu.battle.net/sc2/de/game/unit/marine