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

Sigismund 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 skill, as in him among maybe 4 others. Also, he apparently bested Kharn in a duel in the novel, Betrayer, and Sevatar mentioned duelling him for 20 hours before he got tired of no one winning and decided to cheat and headbutt him just to end it. And much like Ahmed Ibn Fadlan in the 13th Warrior, Sigismund lived amongst the World Eaters more than he did amongst his own legion and began to take to their ways, for example, chaining your weapons to your 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.

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 Garviel Loken; "In the far future, there will only be war."

Also, it should be pointed out that in the HH Book, 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)
2. Always ended in a draw
3. Doesn't consider it a loss if his opponent cheats in the fight. (as it did with Sevatar)

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 met his end during the First Black Crusade, being slain by Abaddon in single combat, breaking his winning streak.(Not confirmed)

Tabletop

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 1 wound per turn mathematically during a challenge, which hilariously, is more per turn than 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.