High Invoker Basaleph is a level 80 elite and a member of the Cult of the Damned. He appears in the Cathedral of Darkness during the quest 
[80] Tirion's Gambit. During this quest, Arthas' Frozen Heart is delivered to him in order to be safeguarded. Tirion Fordring intervenes, and destroys the heart after realizing that there is no chance of redeeming Arthas. The explosion caused by destroying the heart wounds Tirion and the Lich King, and kills High Invoker Basaleph.