The Jolly Roger was the ensign flown by a pirate ship preceding or during an attack, during the early 18th century (the latter part of the Golden Age of Piracy). The vast majority of such flags flew the motif of a human skull, or “Death's Head”, often accompanied by other elements, on a black field. The flag most commonly identified as the Jolly Roger today – the skull and crossbones symbol on a black flag – was used during the 1710s by a number of pirate captains, including Samuel Bellamy, Edward England, and John Taylor. The first recorded uses of the skull-and-crossbones symbol on naval flags date to the 17th century. It possibly originated among the Barbary pirates of the period.

Source: Wikipedia