In the Batman '66 series, a number of villains made their debut, and some kept coming back. One of which was King Tut. While not the most "fiercesome" of Batman's foes, he did always give the Caped Crusader a run for his money.
The sad part about King Tut is the fact that he's actually an esteemed professor of Egyptology, but every time he gets a good thump on the head, he becomes convinced that he is King Tut, and that Gotham is in fact Egypt, which needs his help to be reborn as the "jewel of the Nile". Despite his delusion, he is quite brilliant, even figuring out that Bruce Wayne is Batman, though via trickery, no one believed him. Still, he is a smart villain, and has come very close to finishing off Batman many times.