The history of Christmas and in particular the reasons for the giving of gifts are not known for certain, but several things are known for a fact. The traditions of Santa Claus and giving presents at Christmas time began long before the birth of Jesus Christ, although it really depends on where in the world you live as to how you believe the whole tradition started.
The giving of presents at Christmas time actually dates back over 4000 years to the Mesopotamians. They believed that every year in winter their primary god Marduk would do battle with the evil spirits of chaos. Upon Marduk's return it was necessary for the king to then pledge his allegiance to the God and he would die at the end of the year. The Mesopotamians obviously cottoned on to the fact that they were going through kings quicker than they could produce them, so they would dress a convict up as the king and treat him as though he were a king for one day. At the end of the new year festival they would kill him.
On this day they would present gifts to one another to mark the beginning of the new year and the success that Marduk had yet again bestowed on them. This is where the giving of Christmas gifts began.
St Nicholas is believed to have been born around 300 AD and lived in what is now Turkey. He was a widely revered and loved monk due to his overwhelming kindness. His most famous act of kindness was to save three sisters from slavery by providing them with a dowry in order that they could be married.
As such a popular character he soon became the patron saint of many different groups of people, eventually resting on children and sailors. Traditionally St. Nicholas day was celebrated and remembered on December 6th, although his role as patron saint of children has seen his special day moved to coincide with Christmas.
So one thing that is certain is that Santa Claus visits us on the wrong day every single year. Celebration of Saint Nicholas should in fact be on December 6th, although the moving of St. Nicholas day to the 25th was presumably done to combine his special day with the Christian festival. If the large superstores and toy manufacturers were given the choice I'm quite sure they would rather celebrate them separately, so be warned for next year.