The popular figure of Santa has many names and has his origins in several different traditions. The most famous of these names, Santa Claus, is derived from the Dutch name of Sinterklaas. In the Netherlands there was a long tradition of an elderly, white-bearded man who would bring gifts for children on 5 or 6 December. This itself, like some other similar names, goes back to the 6th century saint, Bishop Nicholas of Myra, an early Greek Christian who lived and worked in an area of what is now Turkey. Bishop Nicholas was known for his charity and especially for liking to give gifts in secret, and even now in some countries it is the tradition for children to leave out a slipper or sock for ‘St Nicholas’ to fill with gifts on 6 December (his official saint’s day) rather than, or as well as, Christmas Eve. In some countries, like Germany, it used to be typical to have a ceremony called the feast of St Nicholas where ‘good’ children were given a nice present and less good ones were given something like a piece of coal or even a stick. This idea is sometimes found today as well – many young children believe that Santa (or Father Christmas) will bring them better presents if they behave well.
In the early centuries in which Christianity was spreading throughout Europe, some other elements got mixed up with the story of St Nicholas and his gifts. Among these were probably old Germanic and Scandinavian legends of gods such as Odin, whose feast was also held at midwinter and who was said to have travelled across the sky as Santa is said to do in his sleigh. The idea of the sleigh and the reindeer also come from northern and Scandinavian traditions.
If we think of Santa today, we probably think of a friendly old gentleman in a red and white suit, with a big bushy white beard. This idea can mostly be traced back to North America in the 19th century, though its origins can be seen in some of the older traditions, like the old Dutch gentleman mentioned earlier (or the ancient – and of course bearded – gift-bringing goat that could be found in some ancient Scandinavian folklore, but which has disappeared today apart from a goat figure often being used as a Christmas decoration). Another influence may be the English figure of Father Christmas, who appeared around the 16th century and was seen as a stout man dressed in red or green – probably a connection with the Christmas colours which were traditional even then and based on the holly and its berries – as the feast of St Nicholas was not significant in British or English culture. Father Christmas was more about feasting and jollity and was not especially associated with gift-giving until his legend began to merge with the Santa story.
In the early 19th century some writers and artists in the US and Canada began to create the Santa that we know today. One book published in 1812 referred to ‘old Santeclaus’ and a few years later the still famous poem ‘A Visit from St Nicholas’ was published. Many of the elements of a modern Christmas can be found here, such as children thinking about being given sugar plums, Santa riding on a sleigh, coming down the chimney and so on. By the middle of the 19th century illustrators were creating pictures of the big, jolly red-coated Santa that we know today. It used to be said that the red colours were an attempt to get advertising for the Coca-Cola company, but in fact the red-coated tradition is much older than that.
You can find more about the origins of Santa here.