Coel (Old Welsh: Coil) or Coel Hen ("Coel the Old") is a figure prominent in Welsh literature and legend since the Middle Ages. Early Welsh tradition knew of a Coel Hen (Coel the Old), a leader in Roman or Sub-Roman Britain and the progenitor of several kingly lines in the Hen Ogledd ("the Old North"), the Brittonic-speaking part of northern England and southern Scotland. Later medieval legend told of a Coel, apparently derived from Coel Hen, who was the father of Saint Helena and the grandfather of Roman Emperor Constantine the Great. Other similarly named characters may be confused or conflated with the Welsh Coel. The legendary "King Coel" is sometimes supposed to be the historical basis for the popular nursery rhyme "Old King Cole", but this is unlikely.
Coel's name was rendered "Coil" in Old Welsh. It may be the same as the common noun coel, meaning "belief, credence; confidence, reliance, trust, faith" (a secondary meaning is "omen"), derived from Proto-Celtic *kaylo- "omen" and ultimately from Proto-Indo-European *keh2ilo- "whole, healthy; blessed with good omen". Coel is often named as "Coel Hen", Hen being an epithet Hen meaning "old" (i.e., "Coel the Old"). The genealogies give him an additional epithet, Godebog (Old Welsh: Guotepauc), meaning "Protector" or "Shelterer". His name is thus sometimes given as "Coel Godebog" or "Coel Hen Godebog". However, some of the Harleian genealogies list Godebog as Coel's father's name.Geoffrey of Monmouth Latinized the name to Coelus. Some modern authors modernize it to "Cole".
Coel Hen appears in the Harleian genealogies and the later pedigrees known as the Bonedd Gwŷr y Gogledd (The Descent of the Men of the North) at the head of several post-Roman royal families of the Hen Ogledd. His line, collectively called the Coeling, included such noted figures as Urien, king of Rheged; Gwallog, perhaps king of Elmet; the brothers Gwrgi and Peredur; and Clydno Eiddin, king of Eidyn or Edinburgh. He was also considered to be the father-in-law of Cunedda, founder of Gwynedd in North Wales, by his daughter Gwawl. The poem Y Gododdin mentions some enmity between the "Sons of Godebog", possibly a reference to the Coiling, and the heroes who fought for the Gododdin at the Battle of Catraeth.