Zwarte Piet is the helper of Sinterklaas, and climbs down chimneys to put presents and candy in kids shoes on December 5th. Sinterklaas has a lot of these sidekicks, and every single one of them is called Zwarte Piet.
The explanation parents these days give to kids as to why Zwarte Piet is black is that he's not black because he's from Africa, but because he climbs down dirty chimneys. Therefor, his skincolor can be anything but we'll never know since we only see the dirt form the chimney. This is told to avoid racial issues.

Zwarte Piet can best be translated as Black Pete.