The Welsh name for Avalon, but also the name of the Celtic goddess Modron’s father, who was said to rule an otherwordly island. William of Malmesbury places his residence at Avalon.
His name may be echoed in Evalach (Evelake) from the Grail histories.
Sources
Gesta Regum Anglorum | William of Malmesbury, 1125
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century