Santa Claus is derived from the Dutch festival figure St Nicholas, or Sinterklaas.
The story is that St Nicholas is a Roman Catholic bishop who rides over the rooftop on a white horse at night, accompanied by his black manservant. While the children are asleep they bring presents, throwing them through the chimney, or the manservant climbing down the chimney to deliver the presents.
The characters have several influences, but the oldest version of St Nicholas seems to be Wodan. With the christianisation of Europe, festivals were changed to better fit the christian mythology. Witness how the midwinter festivals became Christmas and spring festivals became Easter the latter name itself deriving from Ishtar.
The manservant goes back to Wodans ravens, the white horse traces its origin to Sleipnir. There have been considerable influences over the ages, but this seems to be the oldest origin
