The Adar Llwch Gwin were mythical birds found in Welsh folklore that were believed to be extremely large birds (often falcons, hawks or other raptors) that had the ability to understand human language and would obey their master's will without question.
They are most famous for an Arthurian tale in which a warrior named Drudwas ap Tryffin attempted to use the birds to kill Arthur by commanding them to kill the first man to enter the battlefield only for Arthur to be delayed and thus causing the birds to instead attack and tear Drudwas to pieces when he walked onto the battlefield first.