The Guardian (Sorcerer)

The Guardian (often addressed to as simply Guardian) was a sorcerer who led the Guardian Brotherhood.

Biography
The Guardian was quite enigmatic, and believed that the world would turn upon mages one day, so he prepared for that in advance. He fashioned a helmet to protect his mind from those who would try to subvert it. . He also founded a brotherhood to assist him in his plans.

Later, their fortress was assaulted by demons. Demon Troopers who survived the assault carry the emblems of those they have killed.

In-game
The Guardian is the namesake of the Guardian's Contingency/Guardian's Jeopardy item sets in Diablo III.

Trivia

 * The Guardian's traits and biography appear to be a reference to Magneto from X-Men; the leader of the Brotherhood of Mutants, who was convinced that mankind would one day turn on mutants, and also had a helmet crafted to protect his mind from telepaths (particularly from Professor X).