"Santa Claus" is one of the names given to a being from the 16th century known for operating on Christmas night, using flying reindeer, climbing down chimneys, and disembowling children. (BTVS: "The Body")
Santa Claus lived in the North Pole and was a personal friend to McManus. After McManus was killed in 2003, arrangements were made with his family and his body was transported to the North Pole. (ATS: "Unleashed")
Mythology
Over the years, Santa Claus began to be accepted as a mythological creature who brought presents to children each year. Children were expected to write letters to him detailing their Christmas wishes. He was also believed to ignore children who acted naughty during the year. (BTVS: "The Body") He was also known to transport with a magical sleigh, (BTVS: "Two to Go") and for being fat and jolly. (BTVS: "As You Were")
Members of the Salvation Army dressed up as Santa Claus and accepted donations. (BTVS: "Amends")
During Christmas 1998, Willow Rosenberg joked that "not everybody worships Santa." BTVS: "Amends")
In 2000, Buffy Summers equated Rupert Giles, Riley Finn, and Xander Harris with a fairy godmother, Santa Claus, and Q all wrapped up into one after being shown her new training room. (BTVS: "Out of My Mind")
Later that year, Willow, after delivering a package, joked that she felt like Santa Claus. The only exceptions were the fact that she was thinner, younger, female, and Jewish. She was afterwards referred to by Buffy Summers as "Jewish Santa." (BTVS: "Listening to Fear")
In 2002, Sam Finn equated the legend of the slayer with that of Santa Claus or Buddha. (BTVS: "As You Were")
In 2004, Lorne equated Gregor Framkin's behavior with that of Santa's in an attempt to be intimidating. (ATS: "Smile Time")