White Scars
The White Scars are a chapter of Space Marines that are basically Mongols in Power Armor and on bikes. Their Primarch was known as Jaghatai Khan. Primarily, their specialty is hit-and-run attacks. Due to them sweet bikes of theirs.
They are also known for their sweet mustaches and the scars they make on their faces upon induction into the chapter. Which is introduced into the chapter after Jaghatai was reunited with the 5th Legion, (ie: his legion) as he had recently united the fierce tribes of the Talksar tribesmen. Nevermind that many Talksar did join the legion due to their loyalty to Jaghatai. Also, they only recruit from Jaghatai's adopted homeworld: Mandus Planus. Exactly how the badasses of the Space Wolves only recruit from Fenris. As a result, both chapter's ranks are comprised solely out of awesome barbarians. Thus making the White Scars, along with the Space Wolves, the most dead-hard chapters in the Imperium. Aside from the Black Templars.
They also deviate from the Ultramarine's cum-book, otherwise known as the Codex Astartes. This makes them good people, as they don't take shit from the Smurfs. As a result of this, they call their chapter's Librarians, 'Stormseers'. And that's pretty much it. They also have an aversion to Dreadnaughts, as they see it as immoral to place a warrior's spirit in a machine. Sorta the Grey Knights.
Due to their Mongolian overtones and their belief in a Theistic religion, (if their chapter cult rolls that way) the White Scars would be sorta like Islamic Khazakhs.
Their current Chapter Master, or rather, 'Great Khan' is Jubal Khan.