What do you get when Bill Gates is your Secret Santa?

Gates: Tech billionaire, humanitarian—and Secret Santa

A Reddit user named Rachel got the surprise of a lifetime when she discovered the identity of her Secret Santa: Microsoft founder Bill Gates.

(Read more: Six wearable tech gift ideas )

The billionaire was assigned to her in the website's annual Secret Santa Gift Exchange, and Rachel had known him only as "Bill."

Gates made a donation in her name to the nonprofit Heifer International. He sent a box with a stuffed animal representing the gift, accompanied by a photo of himself in front of a beautifully decorated Christmas tree holding the toy and a note to Rachel. A National Geographic travel book was also in the box.

Buzzfeed has a great recap of her thank you, posted on Reddit. In her parting comment, she apologizes to Gates for including an Apple iPad on her wish list.

Bill Gates, aka Secret Santa?

By CNBC's Cadie Thompson. Follow her on Twitter @CadieThompson.