So according to tradition, Sinter Klaas comes to [wherever you are] by boat from Spain (sometimes Africa) with his trust helper Black Peter (Zwarte Piet). Good children who leave out carrots in their shoes for Sinter Klaas's horse get presents (often little gifts with candy and/or fruit). Bad children get whipped and thrown into Black Peter's sack.
Don't look at me, I just observe this stuff. The one time I went to the Netherlands when I was little was right before Sinter Klaas, so I saw a parade featuring a bunch of people dressed in blackface (which is why we can't celebrate this thing well in America) and passing out candy... and the guy they had playing Sinter Klaas spoke English (probably my absent cousin who was "working" at the time). It was one of the best days of my eight-year-old life.
...and yes, it was one of my biggest fears as a kid during the winter to be kidnapped by a guy in a silly beret and ruffle collar, blackface or not. It got me to behave, that's for sure.
Best viewed in high resolution.