Great Mastiff Corp. said:
H.P. Lovecraft died in 1937. Therefore, the copyright on his works should have had a maximum renewal of up to 1987 (50 years after creator's death). So the Lovecraftian mythos should be public domain.
It's NINETY years, currently. However, the copyright laws at the time were slightly different, requiring active renewal, and the putative rights holders let the copyright lapse. Or maybe they didn't. As I've said, there's a big brouhaha about it.
And on trademark - sorry, you're wrong. Names can be trademarked, and are. They cannot be COPYRIGHTED, of course. The use of "Cthulhu" in any form could be construed as diluting the value of the "Call of Cthulhu" game. You don't need a product called "Cthulhu" to be in violation of trademark - any use which could "cause confusion" or "dilute value" is in violation of current law. "Cthulhu" is not an "artistic expession", though the short story "Call of Cthulhu" is. The story could be copyrighted; the name cannot. (Otherwise, you could claim the name of any character in any story is copyrighted!) Names, short sayings, etc, cannot be copywrited, but that CAN be, and often are, trademarked. Trademark must be actively defended, while copyright is automatic and needs no defense. Trademarks can lapse easily, while copyrights are basically eternal at this point.
Don't believe me? Like I said, try publishing a Tarzan RPG and see how far you get on the basis that the original books are well out of copyright.