The Devil was a malign character of an ancient Earth religion and counterpart to that religion's benign God, and ruler of the mythological underworld Hell, modeled after a figure of Norse mythology.
Other religious characters resembling the humans' Devil are the Klingon Fek'lhr and the Ventaxian Ardra.
While demonstrating her abilities to captain Picard and Lieutenant commander Worf, the imposter posing as Ardra also turned in to the Devil and Fek'lhr. (TNG: "Devil's Due")
- Note: There is may be a contradiction when Kang tells James T. Kirk that the Klingons have no devil, but are familiar with the ways of the Earth devil in TOS:"Day of the Dove"