Gabriel Seth
Gabriel Seth is the Chapter Master of the Flesh Tearers Chapter of the Space Marines and a ruthless though pragmatic man.
Father of the Flesh Tearers
When Seth became the Chapter Master of the Flesh Tearers in 815.M41 he immediately was told bad news by his Chapter's Sanguinary High Priest. The regular attrition on the forces of the Flesh Tearers combined with the degree the Chapter lost its members to the Black Rage the Chapter could no longer recruit enough new Marines to keep replacing losses: the Flesh Teares were going extinct. Seth did not take well to this, but he vowed that if the Flesh Tearers were to burn up there were not going to smoulder out, oh no. If the galaxy was to lose the Flesh Tearers it would do so in a massive conflagation fueled by the bodies of heretics and aliens, mutants and daemons with the massive roll of honor of the Flesh Tearers as the capstone to the grave. And so started the epoch of Gabriel Seth and the Flesh Tearers (which is an excellent band name by the way).
Seth knew that his men were all but frothing berserkers who slaughter anything and everything they run into on the battlefield, be they friend or foe. As such many Imperial Guard and Adepta Sororitas commanders dislike fighting alongside the Flesh Tearers: they were rather likely to turn on their allies and civilians alike (perhaps as some kind of proto-Khornate Knights?) and RIP AND TEAR through them. The Chapter Master descided to aim the zeal towards enemies with less non-targets around: diving head-first into dangerous situations in enemy territories and passing distress calls along to other Chapters who do not butcher entire planets. Thus far Seth's plan is working: those who were out for the Flesh Tearers' blood at first are now praising them, though (of course) some sceptics remain.
Son of Sanguinius
The Flesh Tearers are a Second Founding of the Blood Angels and as such hold the Chapter as first amongst peers. When the Blood Angels called for a conclave of the successor chapters. Seth was at first reluctant to answer, but he quickly figured out he could gain from the situation. When he met with the others as the conclave (and a nearly lethal duel between two Brother-Sergeants of the Blood Angels and Flesh Tearers) Dante revealed that after a big internal conflict (not as big as the Blood Ravens civil war, but damn close) the Blood Angels had lost many of their men. So Dante had descided on two things: to accelerate the Blood Angel recruitment process and that all of the successors were to pay a tithe of Space Marines to their progenitor. Seth told Dante where he could stick it, then went even beyond that by suggesting Dante did the reverse: disband the Blood Angels and distribute their Marines and wargear between the Second Founding Chapters.
Before Dante could relieve Seth of most of his primary and redundant organs a subordinate of the Blood Angels High Sanguinary Priest, Caecus, claimed to have found a solution: he had managed to artificially age a recruit into a fully-able Marine in a matter of weeks. Dante was not amused, but Seth was eager to see if the Priest's claim was true, with the future of his own Chapter in mind. Unfortunately the recruit (called a Bloodchild) was as flawed as the last time the aging techniques were used by Corax, and the Bloodchild succumbed to the Black Rage in the middle of a combat trial and had to be put down. This infuriated Dante and ordered the research on the Bloodchild destroyed. Seth took the chance to approach Dante and made a bold offer: to disband the Blood Angels entirely and make them all Flesh Tearers. Dante told Seth to go fuck himself, but then the alarms went off. Caecus had in a bout of desperation and an offer by one Magos Serpens made a terrible mistake: added blood from the Red Grail to the mix of the Bloodchild's prototypes, which spawned a horde of monstrosities called the Bloodfiends. With a nice trollface Serpens then revealed himself as Fabius Bile and the Bloodfiends broke loose. They tried to defile the tomb of Sanguinius, but with the help of Gabriel Seth and the other Second Founding Chapters the Bloodfiends were destroyed. Seth himself held the Priest Gate with Dante (postmortem analysis by Sanguinary High Priest Corbulo revealed that one in five of the Bloodfiends killed at the Priest Gate died of injuries resulting from a shattered pelvic bone), and Dante finally let out his frustrations, saying that Seth thrived on disorder. Seth put on a huge trollface and admitted as much, saying that he was essentially Dante's watchman: while the Flesh Tearers were the Great Angel's battle savagery, the Blood Angels represented all of Sanguinius and had to be held to a higher standard. Dante also proved that there was no bad blood (no pun intended) between two Chapter Masters when he rescued Seth from a Bloodfiend, calling him "brother" instead of the normal "cousin". Bile escaped with some of the blood of Sanguinius and became a target of the Blood Angels from that day on.
With the Blood Angels more, well, bloodied than ever, Dante repeated his request but added that is was nothing more than that: a request. Seth was the first to step up and repeated the final line of the Flesh Tearers Invocation Initiate to prove his point: if you messed with any of the Sons of Sanguinius, you messed with all of them, and pledged some of his men to the Blood Angels.
Brawler on the Battlefield
Gabriel Seth foregoes the traditional Power Weapon of his fellow Chapter Masters in favor of the Blood Reaver: a massive sod-off Chainsword that in crunch terms allows him to hit at Strength 8 at his regular Initiative with Rending, at the cost of no penetrating power whatsoever. Seth is skilled at combat both with the Bloodreaver and his bare hands and feet, meaning that if he's got the opening, he'll give his target an armored kick to the balls at Strength 4. He can do this to anything that attacks him in close combat, even if it has no balls to kick or is too hard to kick in the balls. Meaning that he'll kick a Dreadnought in the dick despite him not being able to do damage this way, but he can in fact kick a Sentinel so hard in the dick it explodes. Because that's how he fucking rolls: if you're an enemy of the Emperor he's going to cut you in half and kick you in the balls.