Throw the Ball.
The chaos Gods are from Elric, Including the 8 pointed star, coined as a symbol for chaos by The elric series. Ulthuan and Naggaroth are just melnibone and Aenarion Is Elric. The original witch hunter models were Solomon kane models. The Moot and halflings are the shire and Hobbits. Sigmar is Conan and Ulric is Crom.
Beastmen were a race from another series altogether. Brettonia is ripped straight from the Lyonesse trilogy by Jack Vance, interspersed with Arthurian mythology.
The old world is the young kingdoms from Elric. Warhammer use to have gods of order like elric. Malus Darkblade is another take on elric. So is Teclis. Dwarves and High elves are stock Tolkien. The Skaven are Suspiciously similar to the Skeksis from Dark Crystal.
The Carstiens were stolen from an Old Hammer horror film called the vampire lovers and mixed with Dracula.
I could go on.
40k is just Dune, Starship troopers, Alien, 2000AD and blade runner. The Titans and Imperial knights are just a take on Battletech.
Ciaphias Kain is Flashman by george frasure. Gaunts Ghosts are Sharpes Rifles by Bernard Cornwall.
Arbites Are judge dread. The god emperor is a take on the God emperor of Dune and they both use foresight to steer humanity onto the "golden path".