Cadal is the name given in Lawman’s Brut to a treacherous Pict in the service of King Constantine of Britain. In Geoffrey of Monmouth’s version of the tale, and in Wace’s Roman de Brut the Pict is unnamed.
The Pict, whom Lawman names Cadal,is said to be one of King Constantine’s most trusted knights. He draws King Constantine apart into a thicket or orchard pretending to have something to tell him privately and suddenly stabs him to death with a knife. Lawman says clearly that Cadal pierced into the heart. Then the Pict escapes in flight.
But many a time have I heard tell that it was Vortigern who caused Constantine to be slain.