Nearly Headless Nick, prior to his death in 1492, was know as Sir Nicholas de Mimsy-Porpington. Nearly Headless Nick is the Ghost of Gryffindor House. While attending Hogwarts, he was sorted into the Gryffindor House and never achieved high marks in transfiguration.

He was born and lived during the 15th century and was born to a royal family. Before he died he was a wizard of the royal court as an adult, which gained him the title of Sir. He was knighted and was a courtier at King Henry VII's royal court.

Sir Nicholas met Lady Grieve while strolling in the park on the evening of in October, 1492. She was certain he could straighten her crooked teeth, but his attempt to do so backfired, causing her to grow a tusk. Sir Nicholas was immediately taken into custody and sentenced to death as a result of this mistake. Before being locked in a dungeon, his wand was taken from him, thus preventing him from using magic to escape. Throughout the night he cried that he would soon undo the damage done to Lady Grieve.

A priest came to Sir Nicholas's cell to comfort him and escort him to the execution site at dawn. He became a "gibbering wreck" when the executioner told him to kneel before the block. However, the executioner's  axe was blunt, as the grindstone used to sharpen it had been misplaced. Thus, it took forty-five hacks to kill Sir Nicholas, and even then his head was only partially severed.

 Since then, he is the resident ghost of Gryffindor Tower. Sir Nicholas chose to linger as a ghost rather than "go on", because, by his own admission, he feared death.  "Nearly Headless Nick", as he was called by the majority of the student body, was always happy to point new Gryffindors in the right direction when late to class.