Quelen

Quelen was a Guardian of Azeroth who researched the. He was unusual in that he involved 's caretaker, in every aspect of his work. According to the castellan, the fel destroyed Quelen because it made him paranoid and insecure. Moroes admitted that his love for Quelen made him hesitant to admit that Quelen didn't possess the strength of will that has. As such, he gave Medivh Quelen's journal and the new Guardian continued the research.

Given the fact there's new Guardian, he is very likely deceased.