From the Roman
cognomen Valentinus, which was itself a derivative of the cognomen
Valens meaning
"strong, vigorous, healthy" in Latin.
Saint Valentine was a 3rd-century martyr. His feast day was the same as the Roman fertility festival of Lupercalia, which resulted in the association between Valentine's Day and love.
As an English name, it has been used occasionally since the 12th century. It is the name of a central character in Shakespeare's play The Two Gentlemen of Verona (1594).