Januarius (also called Gennaro of Naples) had the misfortune to be the bishop of Benevento, Italy at the beginning of the fourth century. This was the time of the persecution of Diocletian. Some deacons were arrested and imprisoned; being a dutiful servant of the Lord, Januarius visited them and prayed with them. There would be no surer way of getting busted for Christianity than praying right in front of the prison guards.
He was sentenced to death and thrown to some hungry bears, but the animals wouldn't touch him. Perhaps it was a miracle, but I'm beginning to think that there were so many Christians thrown to the beasts that eventually they got glutted and lost interest. Certainly bears had to be careful not to overindulge -- they wouldn't want to die from a surfeit of Christian.
Since the bears wouldn't kill, someone was sent in to behead the Bishop. That always worked (though in the Middle Ages the bodies sometimes picked up the heads and walked away). A woman named Eusebia was able to save a bottle of Januarius' blood. You can see this depicted at right; Januarius' head is off and Eusebia holds a little vial up to the leaking stump.
The blood dried up, of course, but every year since 1389, it liquifies on his feast days and on the first Sunday in May. Liquefaction of blood occurs in other churches in the Campagna region of Italy, but seems to occur no where else in the world. The two little crystal vials of blood are held in a bank vault until the feast days.
Januarius is the patron of blood banks and also of Naples, Italy. Give blood -- save some lives.