Hyeonmu is the Black Tortoise, the northern guardian among the four directional beasts (Sasin). It is often pictured as a tortoise entwined with a serpent, and paired with winter and the element water it symbolizes stability, longevity, and protection.
It is the same directional guardian known in Japan as Genbu. Its roots reach back to ancient Chinese mythology, but within a Korean culture that prized the turtle it features prominently in tomb murals, settling into the role of the beast that wards the north.