Gareth is a Welsh name of unknown origin, perhaps from the Old Welsh 'Garw', meaning 'gentle'. It was popularized during the Middle Ages through the tale of Gareth and Lynette in the Welsh romance 'Owain, or the Lady of the Fountain'. Gareth rose to prominence in English-speaking countries throughout the 20th century. In Arthurian legend, Gareth is a knight who marries Lynette after saving her from enchantment.
Gareth was quite popular in 1956 with five newborns bearing that name.