Mrs. Claus

Origin
The wife of Santa Claus, she is believed to have been introduced in the short story "A Christmas Legend" (1849) by James Rees (however, realistically, someone, somewhere most likely told their child that Santa had a wife long before that). The idea found its way in several short stories over the following decades until becoming the protagonist of "Goody Santa Claus on a Sleigh Ride" (1889) by Katherine Lee Bates (Goody being short for "Goodwife" used instead of Mrs.). In Bates' poem, Mrs. Claus wheedles a Christmas Eve sleigh-ride from a reluctant Santa in recompense for tending their toy and bonbon laden Christmas trees, their Thanksgiving turkeys, and their "rainbow chickens" that lay Easter eggs. Once away, Mrs. Claus steadies the reindeer while Santa goes about his work descending chimneys to deliver gifts. She begs Santa to permit her to descend a chimney. Santa grudgingly grants her request and she descends a chimney to mend a poor child's tattered stocking and to fill it with gifts. Once the task is completed, the Clauses return to their Arctic home. At the end of the poem, Mrs. Claus remarks that she is the "gladdest of the glad" because she has had her "own sweet will".

She has since appeared in multiple literature stories, comic books and (less oftenly) in film and television.

In some stories, her and Santa also have a daughter.

Public Domain Appearances
Anything released prior to 1923 (and many more after that as well). In essence, stick to her being Santa's wife, maybe give them a daughter, have them on the North Pole, and do whatever else you want and you'll be fine!