"I live to tell the tale, however, of the Iron Warriors' final victory: The last loyal triumph of the IVth Legion."
- – Barabas Dantioch
Warsmith Barabas Dantioch more commonly referred to as Dantioch was the highest ranking member of the Iron Warriors who stayed loyal to the Emperor during the Galactic Chaos Dumpster-Fire 30,000. The classic cantankerous old general, he linked up with other loyalists at Ultramar and joined forces with the Imperium Secundus. He was attached to the Ultramarines 199th Aegida Company, who would later become the Scythes of the Emperor in the Third Founding; their Chapter Master wears his helmet as a symbol of authority. Oh, also he worshiped the Emperor before it was cool and openly allowed the worship of Big E at his citadel. He is significant to the 40k era in two ways, one for effectively founding a chapter of Iron Warrior successors within Ultramar, and for accidentally calling something to the Milky Way Galaxy 10,000 years after his glorious death. He is also significant for being BFFs with "Crimson Fist" Alexis Polux of the Imperial Fists legion, showing that for all their Primarchs' animousity towards one another, the warriors of the IVth and VIIth legions really could be sincere brothers-in-arms with each other after all.
Back in the heyday of the Great Crusade, He was Daddy's favourite, being promoted to Warsmith at some point. Things were going pretty good, until Dantioch was put in charge of a grand company to take on a migratory Xenos race known as the Hrud. Apparently the Hrud had an "entropy field" that caused things to age at an incredible pace, causing equipment to rust to unusable levels, and bunkers to collapse under their own weight, and even nearby non-Hrud living beings to rapidly age and even die from old age. This proved to be a great hindrance for an equipment-heavy Legion like the Iron Warriors (or any Legion for that matter) and the Hrud took half a Grand Company and a subsector with them before most of their species met the business end of the Iron Warriors' bolters, plasma cannons, and missile launchers, and leaving Dantioch extremely aged (despite his "only" being 200 years old, which is still in the prime of life for an uninjured Astartes) and with a borderline-decrepit body due to the rapidity of his cell decay. This either indicates Astartes can die of old age (or at least be so weakened by it they might as well be) or that the Hrud's entropic field worked too quickly for Astartes biology to keep up with. After that single poor mark on an otherwise stellar career record (and also because he dared suggest that simply throwing more men at a given problem until it budged wasn't the smartest thing to do), Perturabo pulled a Lion El'Johnson and Luthered his ass to garrison duty. Banished to an outpost that was far enough into the Imperium to definitely not get any action, Dantioch spent his time on his magnum opus, a citadel that would make even his own Primarch squeal with delight and jealousy both. This culminated in Schadenhold: A subterranean fortress located on a Death World, suspended upside down over a lake of promethium.
Eventually the whole Horus Heresy thing came along and that out-of-the-way outpost he was put in command of became essential to Horus' campaign to reach Terra, as the outpost could easily become a rallying point for the Imperial Navy if the Traitor Legions overextended themselves. Warsmith Krendl, Dantioch's replacement, showed up with a detachment of Iron Warriors with the backing of a Son of Horus detachment demanding that he cede Schandenhold to the Traitor Legions. Dantioch promptly told them to go fuck themselves with the backing of an Ultramarine champion before settling in for a long siege. Throughout said siege, which lasted a little over a year, Dantioch proved himself the greatest troll since, or rather before, Creed. Doing such things as painting Dreadnoughts black and hiding them in dark corners, breaking the dam that contained the lake of promethium, thus drowning hundreds of traitor guardsmen, then proceeding to light the lake on fire, thus incinerating hundreds more guardsmen and dozens of Basilisks. The siege culminated in Schadenhold being overrun by Krendl's men and an Imperator-class titan, before Dantioch committed the ultimate act of trolling: he detonated the ceiling of the cave system Schadenhold was in, in a defiant middle finger to Perturabo, before teleporting onto Krendl's ship and flying off into the sunset.
Later, he set up shop in the Imperium Secundus, pledging loyalty to Rowboat Gigolo. He died defending the Pharos, the Astronomicon Mark 2, on the planet Sotha from a Night Lords siege, chronicled in the Horus Heresy novel Pharos. In the process, he decided to fall back on his tried-and-true method of "if we can't have it, obliterate everything," pushing the interstellar beacon into maximum overdrive, in an attempt to bathe the Night Lords in a lethal amount of radiation. For his sacrifice, Dantioch was named a "Hero of Imperium Secundus" by Rowboat himself, who also gave Dantioch's remaining loyalist Iron Warriors sanctuary in Ultramar. It is heavily implied that their gene-seed descendants eventually formed the Scythes of the Emperor successor Chapter (who were "officially" declared to be Ultramarine successors and whose chapter master (before he got nommed) bore Dantioch’s unique helm that he wore to hide his age-related disfigurements). A distraught Polux for his part did his late brother-in-arms one final honour, bearing Dantioch's funeral bier alone, as this was the second time he had lost a brother-figure dear to him (the first being the death of his biological brother Helias Polux).
In the end, however, Dantioch's final legacy would end up being a dire curse to plague the entire Milky Way Galaxy, as no one at the time, not the Emperor, not Eldrad, perhaps no one in the galaxy except the Chaos God Tzeentch himself, could have foreseen the apocalyptic consequences of Dantioch's last living act 10,000 years later. It turns out that The Powers That Be have pretty much confirmed that Dantioch's supercharging the Pharos device is what initially caught the attention of the extragalactic Tyranids, resulting in their making a beeline for Sotha and in turn almost dooming the realm that he had pledged to protect, and pushing his own successor chapter to the brink of extinction. For such is life (and death) in the 40k universe; even if you are lucky enough to die a true hero, no good deed goes unpunished after all.