While undoubtedly Santa Claus was based in part on St Nicholas and the gift giving legends associated with him, the modern day Santa Claus bears remarkable similarities to other sources.
Thor and Odin
In 9th century England the Saxons honoured King Winter or King Frost. He would be represented by somebody dressed in a fur hat or crown and would visit their firesides. The Saxons believed that by welcoming Winter as a personage or deity the season would be less harsh to them.
With the arrival of the Vikings in England during the 9th and 10th centuries Odin, their chief god, influenced the Winter gift practices. Odin had twelve characters and the one for December was known as Yalka or Jule and his month was called Jultid from which Yuletide derives. The Vikings believed that Odin visited Earth during Jultid on Sleipnir, his eight-legged horse. He would be disguised in a long blue hooded cloak and carrying a staff and a satchel of bread. His companion was either a Raven or Crow. He was said to join groups around their fire and listen to their conversations to see if they were content. He would sometimes leave the bread as a gift at poor homesteads. 
- An elderly man, jovial and friendly and of heavy build.
- With a long white beard.
- His element was the fire and his color red.
- Drove a chariot drawn by two white goats, named called Cracker and Gnasher.
- He was the Yule-god. (Yule is Christmas time).
- He lived in the Northland (North Pole).
- He was considered the cheerful and friendly god.
- He was benevolent to humans.
- The fireplace was especially sacred to him.
- He came down through the chimney into his element, the fire”.
The tomte/nisse is a mythical creature of Scandinavian folklore originating from Norse paganism and in ancient times was believed to be the "soul" of the first inhabitor of the farm. The tomte/nisse was usually described as a short man (under four feet tall) wearing a red cap with a tassel. Nisse were believed to take care of a farmer’s home and children and protect them from misfortune, in particular at night, when the house folk were asleep. Despite his smallness, the tomte/nisse possessed an immense strength. Even though he was protective and caring he was easy to offend, and his retributions ranged from a stout box on the ears to the killing of livestock or ruining of the farm’s fortune. A particular gift was a bowl of porridge on Christmas night. If he wasn’t given his payment, he would leave the farm or house, or engage in mischief such as tying the cows’ tails together in the barn, turning objects upside-down, and breaking things. The tomte was not always a popular figure: Like most creatures of folklore he would be seen as heathen and become connected to the Devil and having a tomte on the farm meant you put the fate of your soul at risk.
The Long Leap
The following is a short summation of the development of Santa Claus in America..
This section is almost entirely excerpted from Santa Claus The Great Imposter by Dr. Terry Watkins.)
Though his name changed, he was always there. Some other well known titles given to St. Nick’s bizarre companion is a demon, evil one, the devil and Satan. One of his dark duties was to punish children and "gleefully drag them to hell."
The Model For Nast’s Santa..