Mongul is physically more powerful than Superman (though the difference isn’t huge, once Superman goes all-out) and is almost invulnerable to harm. In addition, Mongul demonstrates the ability to teleport, though this may be technological in nature. His limited telepathic abilities allow him to communicate in a vacuum and may allow him to bypass language barriers. (Although I suppose he could just be using some kind of Star Trek-like universal translator.) He can project blasts of potent force via his eyes or hands. 

Mongul also has an incredible intellect, allowing him to master and make alterations to even Controller-level technologies. He wears battle armor with some technological enhancements, as well. It doesn’t protect him from harm — in fact it’s less tough than he is — but it contains remote-control mechanisms to operate his starship at a distance (which may be the source of his teleportation), and has technology which allows him to shrink his enemies and place them in dimensional-inversion cubes. These dimensional-inversion force fields (which Brainiac 5 apparently experimented with when working on his own force field technology) prevent escape by warping their interior reality and absorbing any power used against them from the inside. 

As mentioned above, Mongul has access to a very large starship. It can travel through hyperspace at speeds comparable to the pre-Crisis Superman and has sophisticated sensors. The ship has only been seen during his first fight with Superman, but he’s still star-hopping across the galaxy somehow, so I assume he’s still using the thing. 

History

Little is definitively known about Mongul’s history prior to his first meeting with Superman. Mongul claimed to have been the absolute ruler of his home planet, but his subjects were inspired by an ancient holy man (the Akrymandryte) to rebel against him. Mongul was forced to flee off-world to survive the angry mobs. (According to Mongul’s admittedly biased account, the Arkymandryte then supposedly became an even worse tyrant than Mongul had been.)

It is presumed that Mongul did not gain his vast powers until after he fled his homeworld — otherwise, he could have used his powers to suppress the rebellion. An alternative (frightening) possibility is that Mongul’s abilities are typical of his people, and that somewhere in space there’s a whole planet of Monguls. But it is considered more likely that Mongul gained his powers after fleeing his homeworld, and that with those powers he now turned to galactic conquest, the rule of any single world now beneath him. 

Quest for Warworld

Mongul learned of the legends of Warworld, an artificial planet created by an extremely warlike alien race called the Warzoons. Warworld was their ultimate weapon, a mobile planet with weapons of immense power. However, all the Warzoons died off mysteriously, and the last one was found dead at the planet’s control chair by the Largas, an extremely peaceful alien race. The Largas buried him, then kept the device (a crystal key) that could activate Warworld hidden. But the Largas also died out over time, and the last one gave the key to the Martian race, who had once been devastated by a war, for safekeeping before dying. The key was hidden in a crypt on the fourth planet of the sun in the star-system Cygnus, the same system that was home to New Mars. It was watched over by the Martian people under the leadership of J‘onn J‘onzz, aka the Martian Manhunter. 

Mongul apparently made an unchronicled attempt to claim the key and was repulsed by J‘onn J‘onzz. (Given how easily Mongul takes down the Manhunter in their next encounter, my No-Prize speculation is that Mongul’s initial approach was detected by the Martians and that J‘onn led an entire force of super-powered Martians against Mongul. He retreated, and decided to force J‘onn’s ally Superman to help him. That would explain why Mongul then forced Superman to go in his place.) Mongul kidnapped three of Superman’s friends (Lois Lane, Jimmy Olsen, and Steve Lombard) to force Superman to obtain the crystal key. J‘onn detected Superman’s approach, but given their friendship, approached Superman one-on-one rather than bringing an attack force. While the two argued, Mongul had the distraction he needed to overcome the key’s defenses himself and claim it. Even when the Manhunter freed Superman’s friends (as Superman had hoped he could), Mongul was a match for both heroes, and escaped with the key. 

Going to Warworld, Mongul used the crystal key to activate the cybernetic control chair at its core, which through a direct interface allowed the operator to mentally control the vast array of weapons. Superman recruited Supergirl to help attack Warworld, but its arsenal (including skyscraper-sized nuclear missiles) proved too powerful. The duo realized that it was the control chair itself that caused the extinction of the Warzoons, since the neurological stress eventually killed the operator. They deliberately taxed the system until Mongul fell unconscious. 

Warworld’s remaining automated systems still represented a threat, however, so Supergirl breached the defenses by flying through Warworld at supralight speed. Superman followed and set Warworld to self-destruct. He attempted to retrieve Mongul but the would-be conqueror had already teleported to safety.

Death Stars and Sun Eaters

After Mongul recovered, he discovered another weapon that could cause destruction on a galactic scale. The alien empire ruled by Prince Gavyn (the otherworldly Starman) had originally relied on a planet-destroying weapon to blackmail the other worlds of the empire into obedience. The weapon was protected by force fields and hidden inside a star where no one could reach it, but it could be operated by remote control from Throneworld. Mongul then attempts to conquer Starman’s homeworld, murdering the superhero’s sister and forcing his love into marrying him in order to usurp the throne of the empire for himself. However, Superman arrived and freed Prince Gavyn from the dimensional-inversion cube Mongul had imprisoned him in. While Superman attacked Mongul, keeping him too busy to use the planet-destroying weapon, Gavyn used his stellar powers to enter the star and disable the weapon. Thwarted, Mongul again retreated.

Mongul next encountered and murdered a Controller, taking possession of the Sun-Eater the Controller had possessed.  Mongul brought the creature to Earth, planning both to embark on a new campaign of conquest and to gain revenge on Superman. Mongul defeated Superman and held him captive in another of his containment cubes, intending to force him to watch as the Sun-Eater devoured Earth’s sun. While Mongul easily repelled an attack by Supergirl and the JLA, and the Sun-Eater moved closer to Sol, Superman’s pal Jimmy Olsen managed to send a distress call through time to the Legion of Super-Heroes in the 30th century. The Legion sent a squad back in time to help. They freed Superman in short order, and while Superman battled Mongul again (defeating him decisively for the first time, though Superman passed out immediately thereafter), the Legionnaires destroyed the Sun-Eater. 

Whatever prison was devised for Mongul did not hold him long. Now thoroughly consumed with hatred for Superman, Mongul put aside plans for conquest and focused directly on revenge. He attacked Superman in his Fortress of Solitude on his birthday, ensnaring him with a Black Mercy plant. (The black mercy is a plant/fungus hybrid that feeds off a victim’s bio-aura, paralyzing victims by telepathically feeding them a fantasy-life based on their greatest desires. Mongul knew Superman could only get free by sacrificing his greatest longings, a suitable taste of revenge.) Wonder Woman, Batman, and Robin II (Jason Todd) showed up at the Fortress to help Superman celebrate. Wonder Woman fought Mongul futiley while Batman tried to reach Superman and help him throw off the hypnotic trance he was in. Superman managed to break free when his dream of growing to manhood and raising a family on an intact Krypton turned into a nightmare. Enraged and heart-broken, Superman engaged Mongul in all-out battle. Still, Mongul was only beaten when Robin II ensnared him in the Black Mercy’s grip. This left Mongul trapped in a trance, dreaming of his violent and bloody defeat of Superman and conquest of the universe. 

Description

Mongul is a massively muscled, giant-sized alien with yellow skin and bald head. He has only four fingers on each hand (and presumably four toes on each foot). See illos for details. He usually sports an arrogant, over-confident smile. When he gets angry, this becomes a sneering, dangerous grin. 

Personality

Mongul is a ruthless megalomaniac with absolutely no scruples. He is absolutely self-confident, with nothing but contempt for others of lesser power than his own, which is almost everybody. Basically, he sees himself as having no equals, and lesser beings as worthless. Driven by a desire to conquer and humiliate basically the entire universe, this attitude makes it generally impossible for him to have allies or even henchmen. At most he might make use of slaves, or enjoy extorting service from his enemies by threatening those he loves. Ultimately, though, he is a control freak who relies on nothing but his own power and his technology and special weapons.

Despite his megalomania he is very intelligent and a careful planner. Knowing he cannot be everywhere at once, he seeks out technologies which can make his dreams of galactic conquest possible. He does his research and has successfully found and made use of some of the rarest (and most dangerous) objects in the universe. Unfortunately, his megalomania and overconfidence rarely results in foolhardiness. He will at times retreat when his plans are wrecked, rather than fight to no purpose. Those who thwart him will eventually face his vengeance, though. Superman has thwarted him on three occasions, and Mongul’s hatred of him is intense. Currently, Mongul’s plans for conquest have apparently been put on hold while he seeks to humiliate, break, and ultimately destroy Superman. 

Given this revenge streak, it’s interesting that Mongul’s never mentioned seeking revenge on the Arkymandryte and his former subjects. Perhaps he intended to make them an early target for Warworld, but has since been distracted by an even greater desire for revenge on Superman. (Or, as alluded to in the history, perhaps for some reason he’s afraid to go home? He’s not afraid of much of anything, seemingly, but if his people all possess his power levels…)

DC Universe History

Another guy who’d really like to take Doomsday’s place as the Superman killer. I guess the post-Crisis Mongul died, right, and has been replaced by his more powerful son — who has an identical appearance? One suspects that some writer or other just didn’t want him to be dead, so quickly decided to give him an identical son. At any rate, the post-Crisis Mongul has become a major GLC villain — that wouldn’t be out of character for the pre-Crisis Mongul, either. I could see him invading OA to claim the Central Power Battery, for example — one more example of stealing a super-powerful WMD! Mongul would also be a tough fight for L.E.G.I.O.N.

Marvel Universe History

The simplest way to bring in Mongul is to replace his Superman encounters with Thor in some of his interstellar adventures. The Silver Surfer would also be a good fit. He’d also, of course, encounter Gladiator and the Imperial Guard. Clashes with the Xandarian StarCorps, the Spaceknights of Galador, or Quasar when he was Protector of the Universe would also be fun. His power, appearance, and modus operandi (stealing weapons of great power) are pretty close to that of Thanos, though, so it may be tough to use both. If you decide to do so anyway, a fight between the two over some obscure weapon or other seems inevitable.