"Several of the Coen brothers' films feature a character that embodies the archetype of 'unstoppable evil.' In many cases, it is hinted that these characters are inhuman, or feature demonic overtones."
Example #1: Sheriff Cooley (Daniel von Bargen) in O Brother, Where Art Thou? matches the description of the Devil given by one of the characters. He further indicates his otherwordliness when, advised that it would be illegal to hang pardoned fugitives, he sneeringly opines that 'the law is a human institution.'
Example #2: Eddie Dane (J.E. Freeman), the hitman in Miller's Crossing.
Example #3: Leonard Smalls (Randall "Tex" Cobb) in Raising Arizona.
Example #4: Charlie Meadows (John Goodman) in Barton Fink also fit the description of this archetype.
Example #5: In No Country for Old Men, Anton Chigurh (Javier Bardem) personifies the violence and death in a world that Tommy Lee Jones' Sheriff Bell tries to make sense of...but can't.