One US woman's secret Santa this holiday season turned out to be one of the richest men in the world: Microsoft co-founder Bill Gates.
The gift exchange happened through the website Reddit's secret Santa event, in which users swap presents across the country.
A spokesman for Gates confirmed he participated.
Spokesman John Pinette says the billionaire philanthropist wanted to engage with Reddit's community and promote Heifer International, a foundation that provides seeds and animals to people in need in the developing world.
The woman, identified only as Rachel, wrote in a blog post that she was surprised to find out Gates was her Secret Santa.
She received a stuffed cow toy, a signed card, a National Geographic travel book and a $US500 ($A565) donation to Heifer International in her name.
