Who: Gared of the Night's Watch
Gory details: Gared, an experienced ranger, is sent on a scouting mission to track wildings, but that's cut short after his head is quickly and efficiently ripped off by a White Walker.
Narrative importance: Gared's death harkens the return of the White Walkers to the land north of the Wall.
Degree of difficulty: Easy. Bow down, bitches, because murder ain't no thing for a supernatural being that rides dead horses and speaks in screams! (Unless you happen to have fire and/or dragonglass on hand.)
Creative scale: 1