In the Netherlands, the custom of "Sinterklaas", which was brought to the US and became Santa Klaus, predates Christianity coming to the Netherlands and Saint Nicholas was indeed created in order to be able to continue this "heathen" feast.
It's origins are in the Celtic/Germanic midwinter fest of "Yule". During this fest, the god Wodan, rode on a horse, carried a staff, brought gifts to nice children and had devilish helpers who kidnapped the naughty children. This tradition is still strong in northern Europe, which was much less influenced by Christianity.
Santa Klaus lore still has a lot of hints to the pagan origins. For example, the reindeer which pull Santa’s sleigh are called Donner and Blitzen-‘thunder and lightning’ from the Old Dutch ‘Dunder and Blixem’. (Wodan is the Germanic/celtic version of Odin.)