He was a member of the left-handed magicians guild in Toran, where he advocated the idea of using right-handed, or evil Nadzarin magic in combination with goodly magic to gain more power. Generating some support, but unable to sway the Guild as a whole, he set out to ally himself with the Darklords, believing that he was the fulfillment of the warrior/mage prophecy. He fled for the Darklands killing Loren and Storm Hawk on the way and gaining two servants on his way to Kaag: Carag and Allia. He sought out Zagarna and his Nadziranim and, in exchange for their magic, told them about the Feast of Fehmarn. Armed with this knowledge, Zagarna razed Toran, massacred the Kai Lords, and besieged all of Sommerlund. Vonotar's new powers were almost god-like because of his knowledge of Left-hand magic and the infusion of Nadziranim Right-hand magic. This would prove to be Vonotar's high point as he and Zagarna were poised to conquer all of Magnamund.
During the subsequent siege of Holmgard, Vonotar was put in charge of watching the seas to make sure Durenor didn't send help by that route. Using his newly gained dark powers, he took control of sunken battleships and their crews, which became known collectively as the "death-hulks."
Upon learning that the last remaining Kai Lord was heading for Durenor by sea, Vonotar sent his personal assassins (identifiable by the tattoo of a serpent on their wrist) to intercept him. These thugs all failed miserably in their attempts. He then made one last stab at stopping Lone Wolf, intercepting him at the head of his Death-Hulks on the open seas in a battle against the Durenese Fleet, but his undead sailors were no match for the power of the Sommerswerd, and the death-hulks were sunk. Vonotar managed to escape capture, however, and Lone Wolf was able to arrive in Holmgard and destroy Zagarna, Archlord of the Darklands.
Realizing that the other Darklords would blame him for Zagarna's death and hold him accountable for his failures, Vonotar returned to the Brotherhood of Toran to adbuct Loi-Kymar and his Guildstaff, which had the power to teleport the user across great distances. Using this power, he fled to the icy wastes of Kalte. There he became the personal advisor and sorceror of the Brumalmarc, lord of the Ice Barbarians. Vonotar sapped the ruler of his mental and physical strength and eventually killed him, setting himself as lord Brumalmarc and controling the Barbarians through magical collars and bracelets that forced them to obey him without question. Hiding in the massive ice fortress of Ikaya, he plotted his next move.
Though he believed himself safe in his new fortress Lone Wolf, along with several guides, was dispatched on an expedition to capture Vonotar. This expedition proved successful, and Lone Wolf brought him back to Sommerlund where, for his crimes, he was banished through a Shadow Gate to the Plane of Daziarn, a place where no one had ever returned from.
The gate led directly to the Daziarn, where Vonotar quickly established himself. Digging out a corner of the world he ended up on and labeling it his own, he gathered a number of evil creatures to his cause. Most notably, he set himself as leader of the Villains of Sommerlund, five of the most nefarious Sommerlund criminals who had, at one time or another, been cast into the Shadow Gate by the Brotherhood. He later managed to get a hold of one of the Lorestones of Nyxator, and thus cemented his hold over his corner of the Daziarn. He then began planning his return to Magnamund, a plan that the Lorestone composed a crucial part. Exactly how long Vonotar was in the Daziarn is unknown, but it is doubtful it was more than a few months, since the days there equal years in Magnamund.
It is unknown what age Vonotar was exactly. By the time of the Siege of Holmgard, he was aged, with a hump, but he was young and handsome when he left the Brotherhood (where he had risen to a position of some status). The ageing is the result of a battle with Alyss, who was unable to kill him but was able to age him. This was depicted in book 2 of the Lone Wolf novels.
See also: How to Meet Vonotar in Fire on the Water