Leonid was a noble hero until he was killed and later resurrected by the Lich King as a mindless undead. He was present at Stratholme when Ras Frostwhisper gained his immortality.[1] He was eventually freed by the Banshee Queen, and became one of the Forsaken. Mistrusting many if not most of the members of the Forsaken he left them and is now loyal to the cause of the Argent Dawn.[2] He was a friend of the Forsaken priestTrevor who aspires to follow after Leonid.[3]
He looks at his undeath as a malady. An illness that merely requires treatment, hence his loyalties. It is also a great advantage for the Argent Dawn. What better weapon to smite the abominations of the Scourge than one of the "redeemed" undead?
He is revered by his colleagues because of the sacrifices he has made, but the accolades mean nothing to him.