In SMITE's case, the characters come from mythological sources and those sources are public domain. However, the way they're depicted was chosen by the game developer and their depictions are copyrighted by them.
If someone copied the list of characters and made their own game with their own artwork and gameplay and everything, SMITE's creators could do absolutely nothing about it. But if they copied any substantial elements from SMITE directly, then it starts to go in the direction where lawyers start rising eyebrows. At that point it's no longer making original stuff based on the same PD material.
The first version I played was the Commodore 64 version by Mirrorsoft, which actually didn't use the Russian imagery.
The soundtrack was an epic 25 minute synth prog metal odyssey.
Commodore 64 is a very cool computer.