Jamie Bestwick is a BMX rider that has dominated the discipline of vert riding for several years. Being in his late 30s and still winning gold medals, Jamie has pushed the vert discipline forward even as its popularity is fading amongst the X Games and many other action sports events.
He has pretty much won every major contest he entered in the 2000s. Literally. There are only a few 2nd, 3rd, or worse finishes and if he won those as well people would probably quit riding vert and quit watching it and the sport would die. So think about it.
As far as X Games go, that's a bit different. Especially since they don't even have BMX vert anymore. In 2006 he took silver, and in 2005 he won the whole damn thing. He also won the whole damn thing in 2003, in both US and INTL X Games Events. He even did park that year at the INTL event I suppose to get more pro riders in the division and took 9th. He took gold in 2000 as well. That's a lot of gold man.
What makes him this great rider is his height, his style, his extension, and most of all his diversity and use of the ramp. Nobody uses a ramp like he does. He probably hits every panel of wood on the vert ramp in his run. Alley oop tricks from one end of the ramp to the other, back and forth, doing flairs and whips, and a myriad of variation tricks. That's what makes a great vert rider.
He is also damn funny. If you can find a video interview with him or something, watch it.