Rethald

Rethald was a summoner of demons, and claimed he could control any such hellspawn he called. A demon ended up consuming him. Afterwards, the demon has been killed, and its skull was made into a helmet.

Trivia

 * Rethald bears some resemblance to Wilfred Fizzlebang, a gnome warlock from World of Warcraft who possessed exactly the same traits, and suffered exactly the same fate.