Despite having a very popular feast day dedicated to him, not much is known about St. Valentine. In fact, St. Valentine was actually removed from the Roman Breviary in 1967 due to the distinct lack of knowledge concerning him. But, his feast day is still recognized within the Church and he is still regarded as a saint.
There are two main accounts of St. Valentine's life that have been passed down from various sources. The first says that St. Valentine was placed under house arrest by a judge, called Asterius. While under house arrest, St. Valentine began to speak to Asterius about the validity of Jesus. Asterius then tested Valentine, telling the saint to heal the blindness of his daughter and he would believe. St. Valentine put his hands on the girl's eyes, restoring her sight miraculously. Asterius then smashed all his household idols and he and his entire household spent three days fasting before he and all forty four members of his household were baptized. Asterius also released all his Christian inmates.
St. Valentine was then freed from house arrest. But St. Valentine refused to stop preaching and was therefore taken before the emperor as preaching in those days was illegal. St. Valentine however, was quite liked by the emperor. Unfortunately, Valentine's attempts to convert the emperor, Claudius II, were ill met and thus it was declared that Valentine should renounce his faith or be beaten with clubs and beheaded outside Flaminian Gate. He was then martyred.
Other accounts of Valentine's life say that Valentine was imprisoned by Claudius for preaching and helping Christians. These accounts hold that the blind girl he healed was his jailer's daughter, not the judge's daughter. Both accounts state the possibility of Valentine sending a letter to the girl whose sight he restored signed "Your Valentine". People also disagree on whether St. Valentine was a priest or bishop.
Another account is that St. Valentine was imprisoned for marrying christians, helping christians and preaching in the streets. All three were crimes, most especially the first, as newly married men were not required to go away with the army so as to be able to spend time with their new bride. At a time when the army's forces were severely depleted, this was an issue. Some argue that causing this inconvenience was part of Valentine's intent in marrying the couples. Regardless of which legend is true, his existence is confirmed. His body was found outside the Flaminian Gate and his skull can be found at Santa Maria in Cosmedin, Rome. No matter the legend, the 14th of February is considered a day of love and devotion. St. Valentine is also the saint of passing out.