This caused a whole manner of demonic forces to come through the portal onto Mars' moons and the other bases, with two satyr-like Barons taking control of Phobos. In the future, when Union Aerospace Corporation (UAC) scientists were experimenting with teleportation technology on Phobos, they accidentally opened a rift to Hell. Only the Doom Slayer survived, and continued to fight demons for eons, until he was finally locked away in a tomb on the surface of Mars within an unknown universe. The Night Sentinels, along with their champion, an unnamed human known only as the Doom Slayer, were trapped in Hell, where Barons of Hell and other demons launched a relentless assault on them. The Argenta priests turned against the rest of the Argenta, siding with the Maykrs, who struck a deal with Hell for their mutual benefit. They rarely left Hell during the war against the Argenta, who were led by the Order of the Night Sentinels. Some Fireborne Barons were modified into Armored Barons by the Jekkadians, patrolling the outskirts of Immora and becoming feared even by the Maykrs, as their morning star-like weapon could destroy both body and soul. Barons of Hell were the highest of the order of Hell Knights, with one breed of Barons growing larger and snoutless, and another strain of Barons became the Fireborne, evolving in the depths of Hell and feeding off of the damned.

The Barons of Hell came from a demonic dimension called Hell. The blood of the organic Baron breeds is green. In addition, Barons are known to be nearly unparalleled in bloodlust and combat prowess among demons, boasting some of the greatest strength among demonic races under Titans. If they are related to Hell Knights, this could be an extension of the willing subservience to stronger demons that Hell Knights display. Their level of sapience is unknown, but they appear to be in command of at least some demons, such as Hell Knights, possibly through a biological hierarchy, and are known to also serve as royal guards to the current Dark Lord, implying a notable degree of intelligence and loyalty. Beneath their armored skin, their bones and muscular structures appear to be made of magma, like armored Arch-viles, and a fiery blade protrudes from just above the wrist of each arm.

The race of Fireborne Barons, almost identical to snoutless Barons but with a grey, inorganic, magma-infused body, are native to the deeper levels of Hell, where the incendiary matter of Hell fused with them.

Barons are also described as being the highest in the order of Hell Knights, implying a direct relation between the species.

In addition, they lack snouts, with a bony face that appears to better resemble that of the Hell Knights, with small eyes and no visible nose. What appears to be a subspecies of the Barons of Hell, or possibly an evolved form of the original Barons, is considerably larger, and while original, satyr-like Barons appeared to only bear ordinary skin, these Barons bear what appears to be natural armor over their upper torsos, with the same color as their skin. Barons of Hell are capable of creating and throwing green fireballs, and have bodies that are extremely resilient to various forms of damage. The appearance of the Baron of Hell consists of a reddish-pink complexion, muscular, hairy goat-like legs ending in hooved feet, a muscular upper body, a goat-like snout, and two black outward curving horns located on the sides of its head.

Doom 4 baron of hell