Amorggus

Amorggus was a Nathrezim and a good friend of Taedal ever since childhood. He was killed by Archimonde out of simple boredom with a snap of the Demonlord fingers. His unfounded death made Taedal swear vengeance upon the Burning Legion and eventually start the rebellion.

Given that Taedal is known to change his answers why exactly did he decide to leave the Burning Legion, it is quite possible Amorggus had never existed and this heart touching story was completely made up by the Traitor so he wouldn't have to explain his ability to see thorough walls to Lyra Spellburn.