-EDIT- Oops, would a mod be kind enough to move this to
40k discussion?
I'm a bit of an oddity as I didn't start playing
40k until I was 25. I was aware of the game but never knew anyone who played it until me and a bunch of friends made the plunge together. One of the things that attracted me to the game was that the background was just an amalgamation of other fictional worlds I already loved. I think between the young age of many
40k players and
GW legal's stick up the

policy for protecting "their" IP a decent chunk of players don't recognize the influences. This isn't a
gw bashing thread. I enjoy the 41st millennium and it's developed lots of it's own character, but I'm just interested in giving credit where credit is due.
THE BIG 4
Slayer
Metallica
Anthrax
Megade...
...just kidding.
J.R.R. Tolkien's writings (The basis of much of most any modern fantasy lore, and
40k is still basically
WHFB in space.)
Michael Moorcock's Elric Saga
Frank Herbert's Dune series
Roert A. Heinlen's Starship Troopers
And then the less significant ones I can think of, as many didn't exist at the creation of Rogue Trader but elements
Robert Howard's Conan the barbarian
H.R. Geiger's art/The Alien movie series
Verhoven's Starship Troopers film
The Terminator movies
Various Japanese Mecha Anime series
I've ignored the real life historical inspirations such as Margeret Thatcher's adamantium skull or the literary references to Poe, Dostoevsky or Lionel Johnson.
I'm sure some of the bigger sci-fi and fantasy readers can point out a lot more influences than the few I threw out here.