From The Victorian Christmas by Anna Selby:
“The 6 December is the Feast of St Nicholas, a saint whose real history — the little that is known of it — would seem to make him unlikely material for one of the best loved of all Christian saints…. He became a monk, an abbot and eventually the archbishop of Myra and … also became the patron saint of an extraordinarily diverse number of people including the Russian nation, virgins, children, Aberdeen, parish clerks, pawnbrokers, boatmen, fishermen, dockers, coopers, brewers, scholars, travellers, pilgrims, those who had unjustly lost lawsuits and even thieves.
“His transformation into Father Christmas — aka Santa Claus — was a gradual one. Because of his own generosity, he was very much associated with the giving of presents. So on the eve of his feast day, children would put out hay and carrots for his horse and, in return, they would receive a present from him the next morning….
“Present giving in the depths of winter was not just a Christian tradition. The Romans did the same thing during their Saturnalia festival and the Vikings’ Woden would deliver presents in mid-winter, too. And, in Britain, there was the ancient character of Father Christmas, familiar from the mummers’ plays. The Church pragmatically decided to continue the tradition but under the guardianship of a Christian saint. St Nicholas fitted the bill. In fact, there was nothing very saintly about the earlier Father Christmas who was a drinker, fighter and lover!
“But the Victorians reinvented him, spliced him together with St Nicholas, changed his robe from pagan green to cheery red and brought in the reindeer and sleigh.”