Yulyn was a young Atavus. He was the son of Howlyn. He did not share his father's hunger for feeding on humans. His mother fealt that all life was sacred, and she instilled this belief in her son. Right before the Meteor shower that forced the Atavus into stasis, his father made him choose between feeding on humans or death. Yulyn choose NOT to feed on the primitive humans.
Yulyn is unlike his fellow Atavus. His mother opposed the Atavus' choice of making Earth their home as well as feeding on Sentient Life. Yulyn agreed with his mother and refused to feed off humans. Upon waking from Stasis, he was immediately under attack from Sandoval and Tate. He only managed to survive due to the Renee Palmer showing up. After a rocky start (and almost being left to be dissected), Renee Palmer and Yulyn formed a bond. They formed an alliance to see a peaceful solution to the "Howlyn trying to take over the world" situation. Eventually Howlyn was killed during a battle with another Atavus. This left Yulyn in charge of his people. Yulyn was a natural born leader; his concerns were always for what was best for his people.
Yulyn's first appearence was in Season 5 episode 18 "Bad Genes".