That's Jaghatai Khan, primarch of the White Scars. I keep telling people that few remember they even exist.
The Khan is the only primarch that looks completely out of place, his armour doesn't even look like power armour.
Yeah and his hair/face just didn't really seem in line with other SM's. His sword doesn't even look like it's from the right faction, it's more Eldar looking/Piratey looking heh.