Centuries ago, the Boobrie Behemoth terrorized the Highland lochs until Fergus MacTavish, Angus's ancestor and the first Guardian of the Loch, performed an ancient Celtic ritual that bound their fates together. Through this blood pact, the creature's predatory nature was tempered, transforming it from a mindless hunter into a conscious protector of the waters it once ravaged, eternally bound to serve alongside the MacTavish lineage.

Standing three times larger than a normal Boobrie, the Behemoth possesses the ability to manipulate water and weather patterns around Loch Ness, creating protective mists to shield sacred sites or summoning localized storms to drive away those who would disturb the loch's secrets. Its distinctive call can be heard for miles across the Highlands, varying from a deep, bull-like roar that instills fear in enemies to a melodic, almost mournful song that strengthens the resolve of the Guardians. Despite its immense power, the creature is bound by ancient magic to remain within the watershed of Loch Ness and its connecting waterways, serving as both its prison and its domain.

The Boobrie Behemoth serves as the Guardians' most ancient ally, using its supernatural senses to detect disturbances in the barriers containing eldritch forces beneath Loch Ness while communicating through visions and omens to guide Angus MacTavish toward hidden knowledge crucial for preventing the prophesied awakening.