Cthulhu has been in the Public Domain for a very long time, since 1969 I think. 
	But even before that, H.P. Lovecraft himself explicitly stated that he gave permission for others to use his works as the basis for their own.  
	I just wish we had tentacle face options in the game... 
	Of course, doing that runs the risk of Hasbro coming after you for Illithid copyrights, sigh...