Sigismund

For stomping chaos, accept no substitutes.

"He was, after all, the one guy who said "Sure, cool, this Chapter idea is brilliant. But mine will be six times the size of everyone else's, just because I say so. Later, Terrans."" - Aaron Dembski-Bowden

"In the far future, there will be only war." - Sigsimund to Torgaddon, not knowing how right he would be

Sigismund (also known as Siggy-diggy, Sig of the Dump, and Swagismund) is an Imperial Fist from Warhammer 40,000's backstory.

We don't know much about what he did, but during the Great Crusade, he became known for his skill and hotheadedness. He is referred to as one of the best Astartes in close combat, along with maybe 4 others. He apparently bested Khârn in a duel in the novel Betrayer, the two then ended up becoming good friends until Horus fucked everything up, and Sevatar mentioned dueling him for 20 hours before he got tired of no one winning and decided to cheat by headbutting Sigismund just to end the bout. And much like Ahmed Ibn Fadlan in the 13th Warrior, Sigismund lived among the World Eaters more than he did with his own legion and began to take on their ways, for example, chaining his weapons to his arms.

He served as First Captain and equerry to his primarch, Rogal Dorn. However, he royally pissed his father off when he refused the order to accompany the Imperial Fist retribution fleet to Phall. His reason for doing was because the first Imperial "Saint" Euphrati Keeler convinced him to never abandon his father's side. When Sigismund came clean over his motivations, Rogal Dorn disowned him from the Legion.

Prior to the Siege of Terra, he also led a mission to Mars to retrieve as many weapons and suits of armour as was possible since Mars was by that time, FUCKED. Despite really, really wanting to kill everything standing between him and the traitor Fabricator-General Kelbor-Hal, Sigismund realized that the Imperial Fists couldn't retake the planet without reinforcements, ordering Imperial forces to retreat when the forges were surrounded by traitor Titans.

When Dorn joined the Emperor for the final attack of the Horus Heresy, he (or the Emperor, since father and son were potentially not on good terms) chose Sigismund to be the Emperor's Champion and lead the Imperial Fists ground forces in his place. During this time he challenged 1??MORE THAN TWO DOZEN traitor champions to single combat and buttfucked them all without taking any smoking breaks. BOSS.

In addition he is known for his quote from a conversation with Tarik Torgaddon; "In the far future, there will only be war."

Also, it should be pointed out that in the HH Book, Templar, he is described as having never lost a duel. Ever. This means he's either:

1. Never duelled any of the GOOD fighters (aka Primarchs) Primarchs are OP and therefore an unfair opponent for any Astartes. They occasionally say, in novels, maybe a dude could tangle with a primarch because they can't grasp just how OP those bastards are. Sev is regarded as one of the best Astartes close combatants and they basically tied. If the stats in the HH books(so far) are anything to go off of(admittedly not always, like the Primarchs being nerfed so they can still be balanced), then Sig and Sev were the overall best close combatant Astartes period.1 on 1 ruleswise, however, Sev has almost no chance due to lack of Eternal Warrior.
2. Always ended in a draw. This option is possible, although the context didn't seem to suggest this at all.
3. Doesn't consider it a loss if his opponent cheats in the fight. (as it did with Sevatar) Because he cheated, Jago is technically considered to have lost that sparring duel. Besides, if they had been trying to kill each other Sev would have been way dirtier way earlier, but Sig would have been expecting it as well. That duel was all around still a good indicator of their skill in regards to one another.

After the Heresy, the Imperial Fists were divided into four Chapters, in accordance with the Codex Astartes reforms. Dorn placed the most zealous Imperial Fists under Sigismund's command, forming the Black Templars. They promptly set out on their eternal Crusade. (The third Chapter, formed from the more conservative and level-headed Marines, were the Crimson Fists). Those Astartes who fought on the walls of the Imperial Palace became the Excoriators.

Sigismund would fight in the First Black Crusade, where by that point he was over one thousand years old, having fought and killed everything the galaxy could throw at him (and given that it's 40k, that's a lot). Unlike most Imperials, he still believed the Traitor Legions would return, making the Black Templars the only Imperial force ready when the Black Legion invaded. Sigismund later faced Abaddon himself in battle during the First Black Crusade; the outcome is unconfirmed, but given that Sigismund is long dead and Abaddon very much alive by the 13th Black Crusade, well...

Tabletop

Sigismund protecting the Imperium from Hairesy

He received stats in the 3rd Horus Heresy book; Extermination. Showing him to be a close-combat monster:

With Eternal Warrior, Fearless, Adamantium Will, a +2S AP2 weapon, instant death and rerolls to hit when in challenges, 4 attacks at WS7, and forcing successful invulns to be rerolled. He's the nastiest duelist character so far in virtually any incarnation of the rules, barring the primarchs, and one of the few that has a fighting chance against some of the weaker primarchs. Now that some legions, namely Sons of Horus, Salamanders, and Imperial Fists, have access to Eternal Warrior from relics that non-Primarchs can take, he's descended from being an "I win as soon as I wound" button to merely "75% likely to win."

This means, pretty much all legion characters barring Salamander Praetors and Eidlon are fucked as Sigismund is forced to challenge and most legions have nothing, bar their Primarchs, who could stand up to Sigismund and hope to win (excluding terrible rolls).

In fact, even against his own Primarch (or any T6, 4++ Primarch barring Lorgar), Sigismund makes a good stab at it and causes just under 1 wound per turn mathematically during a challenge (what with IWND and all), which hilariously, is almost as much as Dorn's own brother can cause against him. While Sigismund receives 1.25 wounds/turn in return. Which is actually pretty good for Astartes vs Primarch combat.

Forgeworld have released a mini for "death's champion"... Twice... Failing both times at the attempt.