Gunther Prozen was ambitious and nationalistic in what proved to be a dangerously idealistic (and ruthless) manner. He strongly believed in the Zenebas Empire, feeling he understood his father's sense of betrayal and that he could carry out Zenebas' original goal of a unified Empire ruling Zi; while he never knew Zenebas personally, being a boy when he died, he grew up in a world where the Zenebas Empire existed only as a dead nation, absorbed and subjugated by the Guylos (and Helic) lot.
His approach was that of manipulation and betrayal in return, and he seems to have considered things like instigating war and unleashing dangerous berserker mecha as acceptable forms of reaching his goal. While not a particularly kind man, Prozen is at least shown to be concerned for his son's welfare—one of his last thoughts before his death is whether Wolff's naivety will make for trouble in his new role as Emperor.
Similar to his battle story counterpart, the anime version of Prozen is highly ambitious and self-serving, though he appears more motivated by power straight up. He believes the Helic Republic to be nothing but a band of rebels usurping the Empire's land, and desires to rule the Empire and all of Planet Zi. He gradually climbs his way to the top of the political hierarchy, conspiring behind the scenes, stepping on everyone who gets in his way and casting people aside when he no longer needs them.
Prozen is manipulative, feigning concern for the ailing Emperor Zeppelin to gain favor in the eyes of his peers. He stops at nothing to gain what he wants, even hiring assassins to kill the Crown Prince Rudolph in order to take his throne. He appears to hold fascist ideals, believing that only the one who holds the most power deserves the right to rule.
His attempts to capture an organoid led to Dan Flyheight's death—and, in turn, to him adopting the orphaned Raven, whom Dan had found before Prozen attacked. While Prozen initially swatted Raven impassively aside (as Raven was pointing a gun at him, being frightened and angry), he may have been impressed by Raven's detirmination—regardless, from there on he trained Raven as both a son and soldier.
Both the Battle Story and Anime versions of Prozen are associated with the Death Saurer.
Prozen used a Bloody Death Saurer—a special Death Saurer painted red instead of black—as his personal Zoid during the Republic invasion of the Guylos capital.
After Prozen was mortally wounded by Karl Scwartz, he opted to self-destruct the Bloody Death Saurer, wiping out the Guylos capital of Valhalla and killing both the civilians and much of the Guylos and Helic armies in the area. This drastically weakened both sides' military ability, paving the way for Prozen's son, Wolff, to take control of the Central Continent.
The Death Saurer was a legendary Zoid created by the ancient Zoidians. It proved both near-unstoppable and uncontrollable, and was the cause of their near-extinction.
Prozen revived it in secret using Zoid cores gathered by his minion Raven and his Geno Saurer. The Death Saurer proved impossible to control again, possessing Prozen himself with its evil will and posing a significant threat to all of Zi. The Republic and the Empire teamed up to defeat it, Van Flyheight striking the killing blow with his Blade Liger.
Zenebas had two known children. The first, Elena, would later end up hiding her past and running the Republic as Louise Elena Camford, likely because neither the Republic or Guylos lot would have trusted an open Zenebas heir in charge.
The younger, Gunther Prozen, was Elena's half-brother, and born some time before ZAC 2050 to a high-ranking member of the Guylos court. He never knew his father, being raised by his mother and given a no doubt heavily idealized version of his visions for the Zenebas Empire. At a young age, he was witness to Zenebas' funeral, swearing on that day that he would rebuild his father's nation.
Prozen also kept his father a secret, instead relying on his mother's position to become influential within the Guylos court. When the current Emperor died in ZAC 2094, leaving his six-year old grandson Rudolph as his only heir, Prozen was appointed as his regent. He used his new position to take de facto control of the nation, beginning a massive rearmament program. Unbeknowest to the Guylos leaders, he also formed his own units of loyalists and Zenebas nationals, who would later make up the Eisen Dragoons and Prozen Knights (known for their pinkish-red Iron Kongs and wasp insignia).
In ZAC 2099, Prozen launched an invasion via the Western Continent, starting a new war between the Empire and the Republic. The goal of this war wasn't conquest, however, but to allow the two nations to batter each other and deplete their forces. To this end, he unleashed weapons such as the recreated Death Saurer and the dangerously uncontrollable Death Stinger, seemingly caring little for the danger and destruction—or the deaths on both sides, in the latter's case.
When the Helic army invaded the Dark Continent of Nyx in ZAC 2101, Prozen saw his chance. The Eisen Dragoons and the Prozen Knights launched a proper coup, taking control of the Imperial capital, Valhalla, from the remaining Guylos forces. However, the Guylos and Helic forces teamed up, launching a counteroffensive and nearly defeating Prozen's forces. As a last-ditch effort, Prozen activated his own Zoid, the Bloody Death Saurer, to use on the combined forces.
Before he could use the Death Saurer, however, the Zoid was attacked by prince Rudolph in a Saber Tiger, as well as Karl Schwartz in an Iron Kong. While the Tiger was easily defeated, the Iron Kong managed to severely damage the Death Saurer, mortally wounding Prozen in the process. Not willing to be defeated, Prozen deliberately overloaded the Death Saurer, destroying the capital and the two armies to ensure the greater victory of his plan's success: in the aftermath and chaos that followed, his son Wolff Muroa formed the Neo Zenebas Empire, the Eisen Dragoons he'd led forming the core of its new army.
Prozen's first appearance chronologically (shown later in the anime, in flashback) was as the Division Commander of the Third Panzer. Prozen's column had discovered the location of the frozen Shadow. Quickly realizing the possibilities inherently present in the Organoid, he ordered the deaths of the Republic soldiers protecting it, including Dan. Utterly demolishing all but Dan and a few of his best troops, Prozen ordered his troops to charge the Gustav hauling the capsule. While Shadow emerged, having been released by one of Dan's troops, Dan himself charged Prozen's column and self-destructed his Command Wolf, wiping out an entire platoon of Iron Kongs. Prozen somehow survived the blast, escaping with Lieutenant Harden. He happened across Raven, whom Dan had been shepherding. Raven drew Dan's magnum and leveled it, trying to fire. Prozen calmly walked over to the child and slapped the gun from his hand, remarking casually that the safety had been on the entire time.
He must also have been impressed, as Raven soon came under his care, taking up the very name "Raven" only at Prozen's request, his real name having been burned from him at the sight of Ambient killing his family. Raven eventually became Prozen's finest warrior, surpassing Harden and the rest of the then-Commander's guard. Eventually, Prozen rose in rank to become an Admiral and then Regent. Somewhere during that time, his men captured Shadow and brought him before Raven, allowing Raven to tame him.
His ambitions eventually took him to the council that advised Zeppelin II, the Emperor of Guylos. Upon the death of the Emperor, Prozen made little to no effort to convert Rudolph to his scheming, instead simply trying to eliminate him. His plan was thwarted by Rosso, who kidnapped the young Emperor from the grips of the Royal Guard. Undaunted, the scheming Prozen seized utter control of the Empire, even managing to get himself coroneted as the new Emperor, albeit only for a few seconds.
After several attempts to use Imperial assets to kill Van's and Fiona's group, Prozen used a clone of the Death Saurer to create the Geno Saurer and other weapons, and lured the group to the Death Saurer's birthing area. Somehow, he moved it to the capital building and hid it under the grand stage. After declaring himself Emperor, he used the Death Saurer to annihilate most of Guylos' capital.
The timely arrival of Van, Fiona, Irvine, and Moonbay, along with Hermann and a column of Gordoses ultimately prevented Prozen from leaving the area. The further intervention of the Baron of Wings and Storm Sworder crippled the Death Saurer's Charged Particle Intake fan and allowed Van to destroy the monstrosity, seemingly consuming Prozen in the ensuing fireball.
Prozen, presumed dead by most of the characters, was eventually revealed to have survived the explosion of the Death Saurer, somehow merging with its core. Calling himself the Dark Kaiser, he laid dormant in a cavern by the gateway into the Ancient Zoidian capital (and thus the Zoid Eve). When Shadow was killed, he was teleported there and reborn wild—when Raven, Riese, and Specular arrived, the Dark Kaiser tried to have Shadow kill Raven. The attempt failed, Shadow somehow remembering Raven after some fighting.
The Dark Kaiser then brought Fiona under his control, intent on using her to release the power of the Zoid Eve that would allow him to revive and pilot the original Death Saurer. She resisted, however, instead barricading herself behind psychic walls after pretending to be brainwashed. To add insult to injury, the Dark Kaiser found that he'd been used: Hiltz explained only an ancient Zoidian could control the Death Saurer, and that all along he'd only intended for the Dark Kaiser to be a part of its core. Both of them were absorbed along with the Death Stinger's core in forming the Death Saurer (though Hiltz was left thinking and in control, and the Dark Kaiser disappeared), and thus Prozen ultimately died along with it.