Following a random link in a comment on The ISB has led me to the knowledge that Jack Kirby and Alex Toth did character and production design on Thundarr the Barbarian. Kirby did production design and a lot of the villians, while Toth did character designs for Ariel, Ookla, and Thundarr. Not only that, but Roy Thomas and Gerry Conway were on the writing staff.
Holy crap, no wonder it was so good. I wonder if it's ever going to make it to DVD.
ETA: A quick check of Amazon reveals that you can get freakin' Blackstar on DVD, but no Thundarr.