As someone from the Flemish (dutch-speaking) part of Belgium, I can honestly say that is a very US-centric view you have.

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.)

Rather than saying “it’s origins are x” which reads as if it’s either wholly or primarily based on x, I would say “it’s origins include” or something to that effect. To say “it’s origins are” doesn’t acknowledge the weight of Christian influence on the current tradition, as if it was perpetuated without being majorly changed.

As Christianity spread, holidays and traditions from many parts of the world were subsumed by it. The history of the Church showed that it’s easier to change people’s religious beliefs than some of their cultural traditions. If theologically insignificant elements of a pre-existing pagan tradition got rolled into a Christian holiday that doesn’t mean the holiday is “actually pagan” or observers are giving some deference to a pagan god.

That may not have been your message, but I wanted to point it out because I hear that very often by those who apparently have some axe to grind with the Church and come off as if the history of some Christian holidays is a big secret they uncovered.

Saint Nicolas is sinterklass and sinterklass is Santa Claus it's a language and culture issue.

> (Wodan is the Germanic/celtic version of Odin.)

[Wikipedia:] The Old Norse theonym Óðinn (runic ᚢᚦᛁᚾ on the Ribe skull fragment) and its various Germanic cognates – including Old English Wōden, Old Saxon Wōdan, Old Dutch Wuodan, and Old High German Wuotan (Old Bavarian Wûtan), – all derive from the reconstructed Proto-Germanic masculine theonym Wōđanaz (or Wōdunaz).

My personal favorites, missing from this list, along with improbable etymology, are Wudan, Wudang, Wutan and Wutang.

in the UK, I would say (based on my limited view point) that most people call him Father Christmas , but Santa Clause is sometimes used interchangeably

I'm not sure I'd agree at all with this.

You've got to watch https://www.imdb.com/title/tt1401143/ for a laugh.

Odin giving gifts to nice children? Sounds dubious. Is there any evidence for people having believed that?

Also in the Orthodox countries from Eastern Europe, the custom of St. Nicholas giving gifts to the good children and punishing the bad children, on December 6, was certainly existing in the middle of the 19th century (when December 6 was not on the same day as in the Western countries with Gregorian calendar), because it was mentioned in some books dating from that time, but probably the custom existed much earlier. In any case, the custom was not Catholic or Protestant but it existed all over Europe.

However I have no idea about how he was depicted at that time and the custom was strictly about December 6, not the Christmas, and the gifts or punishments were also only for the children, not for adults.