Kor'sarro Khan
Kor'sarro Khan is what you would get if Genghis Khan rode a motorcycle. He is the captain of the White Scars' 3rd Company, and the Master of the Hunt for the White Scars. He wields a special relic blade called Moonfang and rides a bike called Moondrakken. Sammael wishes he was this cool naturally, and has since overcompensated by nixing the last Imperial Jetbike, rocking an AP2 Sword, Eternal Warrior, and a fucking plasma cannon... on second thought, Khan might need to step up his game just in case.
He's also one of the few non-white characters in the Imperium. On the tabletop, he makes space marine bikers troops (which isn't unique, any Captain on a bike can do that), but more importantly, gives his bike-mounted command squad Hit and Run and Furious Charge. He has also killed Doomrider - wait, what?