St Stephen is venerated as the protomartyr, (the first martyr), of Christianity. He was a deacon in the early Church at Jerusalem. He aroused the enmity of various synagogues by his teachings and was accused of blasphemy. He made a speech denouncing the Jewish authorities sitting in judgment on him and was sentenced to death by stoning. His martyrdom was witnessed by St Paul who later became Christian.
He is mentioned in Acts 6 as one of the Greek-speaking Hellenistic Jews who were selected by the bishops to assist the widows by welfare and other means.
Acts 6; 8 provides: And Stephen, full of grace and fortitude, did great wonders and signs among the people.
He distributed food and funds to the widows and poorer members of the community, organizing meals to feed the poor and motivating people to contribute money to help them. He organized the donations by placing clay terracotta boxes in each church, to be broken open on Christmas Eve.
This institution for charity is the source of two customs that prevail down to our own times- the piggy bank, and the name of his Feast Day, which is called “Boxing Day” after the breaking open of the charity boxes, which was kept on that day in his memory.
Blessing of Horses: Catholic Culture quotes from Father Weiser and provides as follows-
“From early times [St Stephen] was venerated as the patron of horses. A poem of the tenth century pictures him as the owner of a horse and dramatically relates how Christ Himself miraculously cured the animal for His beloved disciple. Although there is no historical basis for this association with horses in the life of St Stephen, various explanations have been attempted. Some are founded on the ancient Germanic ritual celebrations of horse sacrifice at Yuletide. Others use the fact that in medieval times ‘Twelfth Night’ (Christmas to Epiphany) was a time of rest for domestic animals and horses, as the most useful servants of man, were accorded at the beginning of this fortnight, something like a feast day of their own.”
It was a general practice among the farmers in Europe to decorate their horses on Stephen’s Day and bring them to the House of God to be blessed by the priest and afterwards ridden three times round the church, a custom still observed in many rural sections. … [There are parades in Sweden, where riders parade through towns singing ancient carols in his honour].
In Poland, horses’ food, mainly hay and oats, is blessed on Stephen’s Day… In past centuries, water and salt were blessed on this day to be fed to the horses in times of sickness. Women also baked bread in the form of horseshoes (Podkovy).
(This article from ‘Venite Prandete’ also contains a delicious Irish recipe for the feast.)