Helbrecht
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Helbrecht: more like... puts on sunglasses... HELL YEAH!
In all seriousness, though, Helbrecht is the High Marshal of the Black Templars, which is sorta like a Chapter Master, except he also gets to command a massive fleet. He's basically the single most independent commander in the Imperium, and he alone decides where the Black Templars will go; he regularly tells the Administratum to fuck off. He also rolls with some 6,000 marines as opposed to the Codex-mandated 1,000, because Rowboat Girlyman can eat crow (the Inquisition knows about this, but, wisely remembering what happened the last time they got in a dick-waving competition with another codex-non-compliant chapter, decided to just whistle nonchalantly instead).
Helbrecht plowed through the ranks of the Crusade fleets jumping from Neophyte where he helped some Sororitas push a warrior cult deep into a continent spanning volcano mountain stronghold, to Sword Brethren for slaying a Warpspawned Vampire that was controlling the Hive World of Cephian IV. From there he fought for decades alongside Marshall Daidin, and took command of his crusade when he died. He eventually became High Marshall and fucked over xenos populations as he declared a new crusade against the Cythor Fiends in an area of space where no one had ever returned from. Many more crusades of extreme rape followed. He also trashed Imotekh the Stormlord's flagship in revenge for being defeated and having his hand cut off. He helped out on Armageddon where he SWORE REVENGE on Ghazghkull and decided to chase him all around the galaxy. Good ol' Yarrick was planning to do the same thing and asked to hang out with the Black Templars. Helbrecht said yes, and thus began the greatest buddy cop movie of all time.
But seriously, he's the incredibly badass commander of the incredibly badass Black Templars, and his sword is made of the sword Rogal Dorn used on Horus' battle barge. People like him for a reason, even though he hasn't really done anything. To be fair, he got his ass beaten several times in duels with other warlords, but it's OK, as he is more of an admiral and general than close combat monster, and therefore is automatically better than Wardian Mary Sues, who slay Avatars instead of doing their jobs as commanders. Besides, he has Emperor's Champions for kicking the shit out of enemy close combat monsters.
Never mind he stabbed a Daemon Prince to death with only a knife back when he was an initiate.
Gallery
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To whoever unfortunate to be his foe, run...
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Sitting like the boss that he is.
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Dat big-ass sword...