That’s a really good question, because very little is known about him. He seems to be a real person, because archaeologists have discovered an ancient catacomb in Rome and church dedicated to him. In 496 Pope Gelasius set up his feast day as February 14 (along with other martyrs) “… whose names are justly reverenced among men, but whose acts are known only to God.” That’s the facts of what we know.
Legends say that the Emporer Claudius II didn’t want his soldiers worrying about wives back home, so he banned solders from marrying. Valentine thought this was unjust, and married the soldiers in secret. When Claudius discovered this, he sentenced Valentine to prison. In jail, Valentine tried to convert the Goth emperor and was sentenced to death. On his way to his execution, he sent a note to his jailer’s daughter signed “From Your Valentine.” The Catholic Encyclopedia tells us that he was first beaten with clubs and then beheaded on February 14, around the year 270 AD. Pope Julius I apparently built a church near to his memory, dating to around the 5th century. The History Channel has a nice short video here.
What are you doing to celebrate Valentine’s Day?