A 4th century Christian bishop named Nicholas, was famous for his generous gifts to the poor. He is portrayed in ancient relics as a bearded robed man.
Parallels have also been made between Santa Claus and the figure of Odin, a god in Germany prior to Christianity. Children would place their boots, filled with carrots, straw or sugar, near the chimney for Odin's flying horse, Sleipnir, to eat. Odin would then reward those children for their kindness by replacing the food with gifts or candy.
Modern ideas of Santa Claus came from the publication of the poem by Clement Clarke Moore's called "A Visit From St. Nicholas" (better known as "The Night Before Christmas"). In the poem Santa is heavyset with eight named reindeer.
In some early images of 20th century, Santa was depicted as personally making his toys by hand in a small workshop. Eventually, the idea emerged that he had numerous elves responsible for making the toys.
Whatever you believe, be a jolly old elf during the visit to your relatives!