Tu'Shan

(He's still a nice guy, mind you).
Tu'Shan is the First Captain of the Fire Drakes, Regent of Nocturne, and Chapter Master of the Salamanders, and sometimes called Tu'shan Shakur. Only three years into the job as Chapter Master, Tu'Shan took the Salamanders to the Second War for Armageddon, and willingly acknowledged Dante of the Blood Angels as Lord Commander of the Space Marines there. When the time came for the final battle, Dante struck the killing blow on the Orks while Marneus Calgar and the Ultramarines defended the hives. This left Tu'Shan and the Salamanders to protect the civilians, a task they took on with relish. This would be the start of a brotastic career as staunch defender of the common people of the Imperium, rivaling that of Logan Grimnar of the Space Wolves. At the same time, Tu'Shan has called out some of the more overzealous Chapters, such as the Marines Malevolent and the Flesh Tearers, over their actions against civilians.
All in all, this makes Tu'Shan one of the biggest badasses in a universe full of badasses. Because he actuallycares. And He's actually a scary looking motherfucker who makes you piss your pants at the moment of seeing his glowing red eyes.