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 can makes space marine bikers troops if he is on Moondrakken (which isn't unique, any HQs on a bike can do that), and gets D3 extra victory point if he slays the enemy Warlord in a challenge. Other than that, he is basically a normal Captain with Furious Charge (which he does not confer to his unit), a Power Sword which also causes Instant Death on to wound rolls of 6 and the ability to make D3 Hammer of Wrath attacks with Moondrakken. But, more importantly, as the Master of the Hunt, if he is the Warlord he gives every White Scars bike unit or unit embarked in a Rhino or Razorback the Scout special rule, who also allows to outflank, consistently altering the way your Detachment work and transforming it into a fast and impredictable army. He has also killed Doomrider - wait, what?