The idea that St. Nicholas had helpers in his annual mission to spread joy to children seems to be a relatively recent one, although it's hard to tell. Wikipedia says that the earliest known helper for Nick was a captive devil, who presumably evolved in the nineteenth-century Netherlands to Zwarte Piet, or Black Peter. He was commonly portrayed as a Moor, and people portraying him even today do so in blackface. I've heard one version of the story in which Pete goes down the chimneys prior to St. Nick, since he's already black, and hence the soot wouldn't show on him. He's sometimes portrayed as assisting the saint in distributing gifts, but sometimes is also seen as Nick's dark counterpart, stealing away the bad kids, or giving them switches in place of treats. While Peter was originally one guy, it's said that the Canadians decided there should be several of them, and perhaps this was the origin of Santa having a staff. Nowadays, we typically know his helpers as elves, which is a little weird, as I get the impression that the original elves of Teutonic folklore were typically portrayed as rather nasty, rather than helpful. But words evolve, and popular culture these days generally portrays elves as cute little guys with pointed ears, unless they're following Tolkien's take on Elves as tall, skinny, and stuck-up (but still with pointed ears). Some sources from the early part of the twentieth century, however, refer to the helpers by different names, including brownies, fairies, and gnomes. Perhaps the idea of elves as workers is related to that of tiny magical creatures who do household work unless they're given clothing, as in the Grimms' story of the shoemaker and the elves, and the house-elves in the Harry Potter series. In The Life and Adventures of Santa Claus, Santa receives four helpers: a Fairy, and Pixie, a Ryl, and a Knook (the latter two being types of immortals that Baum invented himself). In what was probably a nod to tradition, the Knook's name is Peter, but there's no indication as to whether he's black. When Santa shows up again in The Road to Oz, he has an entire staff of Ryls and Knooks helping him. The Rankin-Bass television adaptation of Life and Adventures also brings in a Sound Imp named Tingler as an assistant to Claus.
Santa's main animal helpers are the reindeer, and they also don't date back all that far, their first known appearance being in "A Visit from St. Nicholas." The poem also established their names, although I understand that the earliest versions refer to the last two as Dunder and Blixem. I'm not sure whether the reindeer or Santa's Arctic home came first, but I know some sources referred to his home as being in Finland, before his residence at the North Pole was established. Baum placed Santa in the Laughing Valley of Hohaho, rather than at the Pole, but kept the reindeer. In his version, there are ten, and their names are different from the ones we all know today.
That Santa is married is also a pretty new idea, which makes sense, because why WOULD a Catholic bishop be married? Besides, the popular name "Mrs. Claus" is kind of absurd, as "Claus" wasn't intended to be a surname. At least according to Wikipedia, Katherine Lee Bates introduced "Goody Santa Claus" in a poem that she wrote in the late nineteenth century. Some European countries have traditions of women who fulfill the same basic role as Santa, like St. Lucy and La Befana, but a female counterpart is hardly the same as a spouse. Mrs. Claus's role in popular culture is probably largely due to her appearance in several of the Rankin-Bass specials. In Santa Claus Is Coming to Town, her name is Jessica, and she has a psychedelic freak-out upon realizing she's in love with Kris Kringle.
I'm hoping to focus on Jack Frost and Father Winter next weekend, and then the Saturnalia after that. Stay tuned!