From saint to jolly old guy

"The name Santa Claus has his roots in the informal Dutch name for St. Nicholas, Sinterklaas (an abbreviation of Sint Nikolaas). St. Nicholas was a historic 4th-century Greek saint (from an area now in modern day Turkey) who had a reputation for secret gift-giving, such as putting coins in the shoes left out for him."

St. Nicholas “Lipensky” as he appears on a Russian icon dated to 1294 from Lipnya Church of St. Nicholas in Novgorod

"Being the patron saint of children St. Nicholas has long been associated with giving gifts to children. The parallels to the modern day Santa Claus don’t end there. In his Dutch form of Sinterklaas he was imagined to carry a staff, ride above the rooftops (on a huge white horse) and have mischievous helpers who listened at chimneys to find out whether children were being bad or good. These features all also link him to the legend of Odin, a god who was worshipped among the Germanic peoples in North and Western Europe prior to Christianization."

http://publicdomainreview.org/collections/a-pictorial-history-of-santa-claus/