According to Geoffrey of Monmouth, a king of Britain in the third century BC. He was the son of King Danius and Tangustela, a concubine.
He would have been of highest renown for his prowess had he not given way to exceeding great cruelty, for no man would he spare his wrath, but would slay him on the spot had he any weapon at hand.
During his reign, Britain was invaded by Flemmings. Morvid defeated them and brutally executed them. He died fighting a ferocious sea monster who had attacked the island.
Morvid had five sons named Gorbonian, Arthgallo, Elidur, Iugenius, and Peredur. Gorbonian succeeded him.
Source
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138