Taran met Llassar and his father Drudwas Son of Pebyr at Commot Isav, one of the smallest Commots of that free-born region. The men of the village were meeting about an ensuing raid on the community by Dorath and his ill-favored band of sell-swords. Taran suggested a plan of defense that would surprise the spoilers and turn them away. The men -- including Drudwas and Llassar -- agreed to the plan, despite Taran's being a stranger to them.
In the prelude to the raid, while waiting together in a stable, Llassar reminded Taran of himself at that age. During the raid Llassar took a knife on Taran's behalf from Gloff, but survived the wound. Dorath's band were either killed or scattered.
When Taran returned to the Free Commots flying the war banner of the White Pig, Llassar joined his rising army. It was Llassar who said that the Commot folk rallied "to the banner of the White Pig because ... it is the banner of our friend Taran Wanderer".
Llassar's knowledge of mountainous terrain helped Taran's party keep pace with the army of Cauldron-Born and hinder them along their path through the Hills of Bran-Galedd. If not for Llassar's skill as an upland guide, it's likely Taran would never have interceded between the deathless warriors and the Sons of Don in their assault on Annuvin. Llassar fought in the battle that ended with the destruction of Arawn Death-Lord.