Morvael

Morvael the Impetuous was the ninth Phoenix King of Ulthuan. He would also be the first to commit suicide, having been driven insane by years of paranoia and sabotage.

History
Prior to ascending the throne, Morvael had been High Loremaster of the White Tower of Hoeth (although originally from Yvresse). He was not well versed in statecraft or warfare. His first act was to order a punitive attack on Naggaroth to avenge Aethis' murder: unfortunately, the army he sent was massacred as it made landfall (an event the Druchii fondly refer to as "The Day of Blood"), and word of its failure spread panic across Ulthuan. It transpired that, far from being an extinct race, the Dark Elves had simply been amassing their strength for a return to hostilities with the Asur, and Malekith took advantage of the reduced military presence to once again assault Ulthuan. Having learned from his mistakes, Morvael appointed Mentheus of Caledor as his field commander of the Asur armies, and introduced the levy system, requiring that every Elf spends part of the year as a soldier. As Mentheus won the war, Morvael became ever more despondent at the high cost in Asur lives, and was driven deeper into paranoia and insanity through horrific nightmares Malekith's sorcery inflicted on him. During the final assault on Anlec, Mentheus’ forces took the castle, but Mentheus himself was killed: his dragon, Nightfang, went berserk and broke the back of the Druchii armies, and the survivors fled back to Naggaroth, Malekith in the lead. Weary beyond bearing, Morvael committed suicide by walking into the Flames of Asuryan once again.

Source

 * Warhammer Armies: High Elves (4th Edition) -- pg. 7, 16-18.