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 circa Fourth Century CE 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".