Gwallog ap Llaennog (several Middle Welsh variant orthographies include Gwallawc fab Lleynawc ; standard Welsh : Gwallog ap Llëenog or Llëynog) was a hero of the Hen Ogledd. He has long been considered a probable sixth-century king of the sub-Roman state of Elmet in the Leeds area of modern Yorkshire, though some more recent scholarship would identify him more tentatively simply as a 'king of an unidentified region in the north'.