阎王 (Yama) was borrowed from Indian Buddhism into Chinese folk religion. He judges the dead in the underworld (阴间). The full form is 阎罗王 (Yánluówáng).
usage
Often used figuratively to describe a terrifying authority figure. The saying 阎王好见，小鬼难缠 means 'the big boss is easy to deal with, but his underlings are troublesome.'
