If you're talking about ring names, it's a trademark. Billy Gunn actually owns his name now because WWE forgot to renew it. Everything else pertaining to the character would be IP. IP when it comes to wrestling is harder to enforce so usually WWE usually goes after wrestlers for using their trademarks. Hence why Billy is still basically Mr. Ass, which he doesn't own, just the name. But, then again, I hear WWE has loosened up when it comes to fighting people barely making $100 off their IP now. AEW, though, they'll be more vigilante, probably.