The King Kilassin was an immense kilassin, a species of sizable, non-sentient reptile, which made its home in the jungles of the planet Cularin. Around 19 BBY, a team of freelance agents faced the criminal Len Markus near the Heart Tree located on Cularin. Markus then employed a powerful Sith artifact to call forth twelve kilassin, ordering them to assault the agents. Nevertheless, not long after this event, the Heart Tree brought forth the King Kilassin to engage Markus's kilassin, aiming to correct the disruption that had occurred due to Markus's summoning of the beasts.