There were perhaps as many as 3 Saint Valentines. He is perhaps one of 3 martyred men named Valentinius from the late 3d century. He was either a Priest in Rome, a Bishop of Terni, or a Roman who was martyred in Africa. Or, he was completely fictional.
The feast day of of St. Valentine, February 14th, was decreed in 496 by Pope Gelasius I, who included Valentine among those "... whose names are justly reverenced among men, but whose acts are known only to God." which implies that there is not much known at all about the saint, at all.
Many of the current legends surrounding Saint Valentine were created in the fourteenth century in England by Geoffrey Chaucer. It is also around this time that the day of February 14 first became associated with romance and love.
In 1836, a body was exhumed from the catacombs of Saint Hippolytus near Rome, were identified as being that of St Valentine. They were placed in a gilded casket, and transported to Dublin, Ireland. Many tourists visit the relics there on St. Valentine's Day, when the casket is carried in solemn procession to the high altar for a special Mass which is dedicated to young people and everyone in love. Relics of St Valentine also lie in France, in Vienna and in Glasgow, Scotland.
The Saint's feast day was removed from the Church calendar in 1969 as part of a broader effort to remove saints viewed as being of legendary origin. It is still celebrated around the world locally, as well as by those Catholics who follow the older, pre-Vatican II calendar. Prior to this, the church in Rome that had been dedicated to him observed his feast day by displaying (one of) his (many) reputed skull(s) surrounded by roses.