I know, right?! Way back when 3rd edition D&D came out with their Open Game License, I went on a quest to find out who owned the rights to Thundarr the Barbarian so I could make a D&D Thundarr campaign book. Never did find out. More recently I did some searching (when 5th ed came out) and I think it's under the umbrella of Warner Bros. Which means it would probably cost me millions to get the rights. Bah.