Sons of Malice
The Sons of Malice are a Renegade Chapter of Chaos Space Marines who are particularly unnerving individuals which have grown infamous amoungst the worshippers of Chaos. Fighting in complete silence, they drag captives off after raids and proceed to eat them, preferably while the captive is alive and fully aware of what is going on. Not for any trivial reason are they looked at as a chapter of Hannibal Lecters in space, or Friday the 13th Jason in space for being a mute killing machine.
Origins
The founding of the Sons of Malice is unknown although they are suspected to be one of the Astartes Praeses, the twenty chapters tasked with guarding the regions around the Eye of Terror and preventing chaos incursions into Imperial Space. They are also assumed to be the missing 11th Legion of Astartes, as their god Malal/Malice's sacred number is 11 and they have 11 main champions.
The Sons of Malice fell when, after a victorious campaign, they engaged in a series of victory celebrations that bordered on cannibalism. While some Space Marine chapters do have their own set of more grotesque rituals (the Blood Angels, for example, partake in literal consumption of blood as a scout's initiation), they're not considered heretical as such rituals are usually part of Astartes tradition. One of the Space Marine gene-seed organs, the Omophagea, is even specifically designed for cannibalism. However, Inquisitor Pietas, the one who observed their victory rites, was unacquainted with such customs, and was horrified by it. Though, to be fair, if the Sons of Malice were cannibalizing chaos heretics as regular rites, then they could very much have been corrupted, since Kroot have gotten corrupted by chaos by eating chaos cultists so there's no reason to believe that doing the same thing won't corrupt Space Marines.
Thinking them corrupted by chaotic taint (and for some reason, never asking other inquisitors or even other Space Marines to confirm it), the Inquisitor, along with a strike force of Sisters of Battle Celestians, assaulted the Sons of Malice chapter homeworld of Scelus. The Sons fell on their attackers with savage anger at the interference with their chapter rites and defeated the Celestians, the captain of the first company dragging the Inquisitor to the chapter's altar and ritually sacrificing her before devouring her.
How lovely.
Needless to say the Imperium was a bit miffed at this and declared the Sons renegades (even though it had been the Imperium to betray the Sons, rather than vice versa). In return the Sons engaged in a hate-fueled war with the Imperium. Needing a powerful patron, the sons found this in Malal, the Chaos God of Terror and Anarchy. As Malal is directly opposed to the other chaos powers, the Sons battle the other worshipers of Chaos with as much hate as they do the servants of the Imperium. Considering this, it is surprising that the Sons have not been wiped out by either the other forces of Chaos or the Imperium, unless they are receiving support from somewhere, but to be fair, Malal supposedly buffs his followers to almost Primarch levels, so at least there's a slight reason they aren't all dead yet.
13th Black Crusade
During the 13th Black Crusade the Sons fought to reclaim their chapter homeworld, Scelus, but were unsuccessful. They did manage to bloody both chaotic and Imperial forces, however. On hearing this it is reported Abaddon did rage greatly but he was unable to do anything without arms and the rage of the arch champion of chaos did please Malal greatly.
Dark Times ahead...
Once every century, the Sons of Malice gather on the space hulk "The Labyrinth" , the closest thing the renegades now have to a homeworld. This holds paramount importance to them and no matter their commitments they return there at the appointed time. They bring slaves of all races to be ritually sacrificed (read: eaten) to Malal. Retreating to their cells with their captives, the Sons practice the lessons of Saint Hannibal and the halls echo with screams for mercy.
Another ritual carried out is the Challenge of the Labyrinth, which a few volunteer to do every century. None are seen again but those that pass the tests are said to become the Doomed Ones, the mighty champions of Malal, enemies to Chaos and Order alike. The Doomed Ones have a special purpose; once there are 11 of them, they will be ritually sacrificed to Malal and this will allow him to manifest in real space and lead his chosen warriors in person. With their God at their side they will unleash a crusade of hate to claim revenge on all that stand in their way. Recently the 11th warrior was chosen and the time of the coming of the Hierarch of Terror is at hand....
Daily Rituals
The Sons of Malice are anti-chaos space marine.
They must not shown anger or else it pleases Khorne.
They must not shown hope or else it pleases Tzeentch.
They must not shown despair or else it pleases Nurgle.
They must not shown enjoyment or else it pleases Slaanesh.
There is only utter silence.
04:00 - The Sons of Malice rise up from their cell in The Labyrinth. The cells is messy from the captive devouring last night and it will took 30 mins to clean up.
04:30 - Morning Prayer. The Sons pray to their renegade god Malal in utter silence.
06:00 - Morning Firing Rites. The Sons conduct target practice on captured imperial/chaos citizens/cultists.
07:00 - Chaos Battle Practice. The Sons release captured daemons align to one of the four gods or chaos champions into an arena and have one of the Sons take them one on one. The remaining Sons that are not fighting instead, learn on fighting daemon via observation behind a steel cage in utter silence. The remaining Sons that were slain by the daemons are to be chopped to bits and served as lunch later.
08:30 - Loyalist Battle Practice. The Sons release strong, captured imperial loyalists (Commissar, space marine, ogryn, even dreadnaught) into the arena and repeat the same thing they did with the daemons.
10:00 - Morning Meal. The Sons devour the left overs from the battle practice AND chaos/imperial/xeno captives. The Sons that did not finish their remaining 'meal' properly are to be sent to rudimentary clean up of the hall.
11:00 - The 2 hours of Hate. The Sons unleash their hatred on the loyalists and the forces of chaos by cursing at their name loud and clear at the "Hall of Tolerance". They will be talking shit on how the Emperor is a shitty false god and Marneus Calgar is a smurf daddy mary sue. For chaos, the Sons will talk shit on how Horus is weak and how Abbadon is an armless failure. The Sons also bitch at the four chaos gods by calling Khorne an autistic paraplegic, Nurgle a fat piece of shit, Tzeentch an OCD-ridden little bitch and Slaanesh a faggy little whore. Drawings are also allowed on the walls of the main hall, but must be done with the blood of imperial/chaos captives. All the above must be done as emotionless as possible.
13:00 - Tactical Indoctrination. The Sons plan on raids and invasion upon chaos territories as well as imperial territories. After it has been decided, the Sons will part ways to their respective planned raid route until 20:00.
20:00 - Returning to Base. The Sons return with human/xeno/daemon captives of various aligns. 50% of the captives are to be sacrificed at Malal's name while the remain 30% are used for the upcoming evening meals and 20% are given to the Sons as a sleeping doll.
21:00 - Evening Meal. The captives from today's raid are consumed.
22:00 - Free time. The Sons use this time to clean their favorite cold steel melee weaponry. Others like to read picture books about human/xeno organs or reading books about the legendary cannibal back in the age of terra, especially a particular fellow called Hannibal Lector. Those with psychic gifts open portals to the realm of chaos and bring in even more daemons for tomorrow's battle practice.
24:00 - Rest Period. The Sons retreat to their cells with their captives. The Sons practice the lessons of Saint Hannibal (in utter silence of course). Those who had broken the silence or shown any emotion whilst doing any of the objectives above are either sacrificed to Malal or forced to participate the Labyrinth challenge.