They are called Jeoseung Saja.

In Korean mythology, Jeoseung Saja acts like the Grim Reaper, escorting souls—both good and bad—from the physical world to the netherworld. Unlike the singular Grim Reaper of Western lore, the Jeoseung Saja are a class of spectral bureaucrats responsible for this task.

The Jeoseung Saja themselves are not individual deities but rather servants under the authority of King Yeomna, the ruler of the Korean underworld. King Yeomna oversees the judgment of souls and determines their fate after death, with the Jeoseung Saja acting as his emissaries, executing their duties with steadfast dedication.