The Roman martyr St Valentine, commemorated on 14th February, the day of his burial
From The Oxford Companion to the Year (1999) by Bonnie Blackburn and Leofranc Holford-Strevens:
St Valentine was a fourth-century Roman martyr with no obvious connection with lovers. The tradition that birds began to sing about this time gave rise in the late 14th century to a belief, attested by Chaucer in “The Parliament of Fowls” and contemporaries both English and French, that they chose their mates on 14 February… This amorous behaviour passed from birds to human beings; in modern times it has been exported to other countries, even Japan, where it has mutated into a requirement for women to give chocolates to men, in particular their superiors at work. Traditionally, a valentine might be chosen for the coming year in one of three ways: according to true desire, by the drawing of names on the day before, or as the first person of the opposite sex encountered on the day.
From the “Hold Fast” sermon by Catholic convert turned Puritan John Gee, 1624:
The Jesuits upon St Valentine’s Day do choose some female saint for their Valentine: one takes St Agatha, another St Clare, another St Lucy… I asked them what they meant to choose such Valentines. They answered me, that in respect of their vows, they could have no Valentine that lived here upon earth; and in regard of their angelical life, they were to choose Valentines in heaven. I asked them, whether they thought those saints knew that they had chosen them… Oh, yes, say they, we shall be honoured all this year by that Valentine we make choice of, and she will intercede for us, and to some of us our Valentine doth appear in visible bodily shape, telling us what to do all year after.
Samuel Pepys writes in his diary:
14th February 1661: Up early and to Sir W Batten’s [his neighbour], but would not go in till I asked whether they that opened the door was a man or a woman, and Mingo [the servant], who was there, answered a woman, which, with his tone, made me laugh; so up I went and took Mrs Martha [Batten’s daughter] for my Valentine (which I do only for complacency), and Sir W Batten he go in the same manner to my wife, and so we were very merry.