Excoriators

Excoriators
Battle Cry	Whip Me Harder!
Founding	Second Founding
Successors of	Imperial Fists
Successor Chapters	None
Chapter Master	Zachariah Kersh
Primarch	Rogal Dorn
Homeworld	Eschara
Strength	~800
Specialty	Defense and attrition fighting, BDSM
Allegiance	Imperium
Colours	White and Silver

The Excoriators are a chapter of Space Marines descended from the Imperial Fists. They are the subject of Rob Sanders' Legion of the Damned novel, more so than the Legion themselves (we get the Legion are mysterious and all, but half the time you forget they're the reason you bought the book). They're basically a chapter full of grumbling whiny killjoys with a pain fetish. Alternatively, you could say they have little tolerance for failure, are stubborn in a bad way, and suffer from a massive guilty conscience. They spend the first half of the novel whining about how badly the Alpha Legion raped their First Company, stole their Chapter Standard, and poisoned their old Chapter Master ("Oh go cry us a river you pussies." ~Lamenters). They spend the second half of the book fighting a blood crusade. They also spend the entire book ordering their chapter serfs to whip them harder, dammit!

They're one of the very few Imperial subfactions with the balls to point out the Emperor never wanted to be worshiped as a god, that he's nothing more than the greatest human psyker. They actually get into an argument with the Ecclesiarchy about this at one point; the argument ended with some Excoriator Scouts sniping the braindead priests who had decided that it was okay to arm and train Redemptionist militants in an open violation of the Decree Passive (here's a protip, Ecclesiarchs: if making threats against Marines gets Inquisitors killed, you won't fare any better).

Excoriators Armor Scheme

They have this gene seed defect called "the Darkness". All it does is make them fall into a coma at random, much like how aneurisms kill normal humans. They actually figured out a cure for this coma though, but after they successfully test it out on Zachariah Kersh, their Chapter Champion, they spend a hundred more pages complaining about how he's still "cursed" and how he's a "coward" for not chasing the Alpha Legion (even though Kersh, who had just been appointed Captain of the Fifth Company by order of the aforementioned poisoned Chapter Master, points out several times that the planet the Alpha Legion are supposedly on is an obvious trap, just like last time) instead of rejoicing that their best swordsman is alive and just beat the motherfucking Black Templars in the Feast of Blades (a swordsman tournament of Imperial Fists successors). Seriously, they waste so much time whining and bitching and indulging in their stupid whipping fetish. This is probably why the Legion of the Damned waited until all of the whiny little bitches are dead before actually showing up in their own book. Kersh ends up being the only Excoriator to survive the battle, and doing so seems to finally earn him some damn respect amongst the rest of the Chapter. He later becomes Chapter Master.

As a side note, "to excoriate" means to harshly criticize, or to scrape away the skin. While that obviously points to their adventures in BDSM, it also shows how impossible it is for them to be satisfied. But then they all died, so maybe they had a point.

Another interpretation

First and foremost let me say this, when Space Marines are the primary characters in the piece it is not a good idea to write them as the utterly stoic fearless killing machines that the rest of galaxy sees them as. Why? Because internal conflict is one of the greatest hallmarks of fiction; without internal conflict the characters are two dimensional cardboard cut-outs meandering about the setting. The Excoriators carefully skirt this line; they have internal conflict to spare, and none of it is arbitrary or stilted. Their real problem is they risk coming across as two-dimensional cut-outs anyway because 90% of them can't move past "grouchy" and "cynical" for their character traits, and because they insist on chasing their stolen Chapter Standard to a planet they already know it isn't on.

Now let's move on to what makes the Excoriators awesome:

They, like most Chapters descended from Rogal Dorn, put an enormous amount of emphasis on endurance, perhaps even more so than that of other Imperial Fist descendants. For example, when their power armor is damaged they will only repair it to the point of restoring functionality. Superficial things like scrapes, pitting, dents, and etc. are ignored. So while other marines (Pretty Marines) will spend hours making sure their armor looks just perfect, Excoriators show up looking like the maw of the warp just spat them out. You want to scare your enemy? Show them that you've already weathered everything they could potentially throw at you. How their champion won the Feast of Blades was not, by his own admission, simply because he was a superior swordsman or duelist but also because the Black Templar and Imperial Fist champions with whom he was dueling with simultaneously underestimated the sheer amount of damage the Excoriator's champion could soak up and still fight like a son of Dorn.

They also have massive adamantium balls. Like, even by space marine standards. Once they're done whining about the Alpha Legion, they grab their bolters and face down a blood crusade, knowing full well they're going to die, without any hesitation or further dissent. There are only 50 marines on the planet (and about 3000 Sisters of Battle), and the crusade has somewhere around 50 ships. One scout gets his legs (it was his pelvis) eaten by a daemon, yet demands to be on the battlefield three days later. Even their serfs get in on the action loading autocannons and shooting laspistols. There's also a techmarine that is constantly followed by his pet thunderfire cannon that spends part of the battle going off on a search and destroy, by itself, through the streets and unloads a metric fuckton of ordinance, point blank, into a bloodthirster.

Also while the Excoriator's are unusual in their denial of the Emperor as a god, the Legion of the Damned heavily suggests that the Excoriators may have come around to the divinity of the Emperor since it was the plea for assistance that was sent directly to the Imperial Palace on Terra that seemed to preempt the arrival of their ghostly saviors. Of course, it's far more likely that the Excoriators will simply figure it was because the Emperor is, you know, a super-powered psyker who is probably always paying attention to calls for help from his Astartes. Truly, "the Emperor Protects".