Old Nick or "Auld" Nick is one of the many slang terms or appropriately enough, nicknames for the devil, Satan, Lucifer or whatever you are most familar with.
The story goes that the Archangel Sammael, first of the Heavenly Host rebelled against God when God placed Adam above the angels in the Order of Creation. Sammel, also called Lucifer Morningstar and the most beautiful of all angels proceeded to war against God.
He was defeated and fell, to become Lord of Hell.
This story is best recounted (in my opinion) in Paradise Lost by the blind poet, John Milton. | 
