Ernst is the interim president of the Federal Republic of Giad. He was a former imperial general disillusioned by the Giadian Empire's policies. He led the revolutionary forces to victory against the Empire, becoming the first president of the Federacy. He is also the adoptive father of Frederica Rosenfort and the five survivors of the Spearhead Squadron.
Ernst is a middle-aged man who has the ink-black hair and eyes of a Jet, though his hair has begun to turn gray due to aging. He wears a pair of silver-rimmed glasses and sports a straight moustache. His physique is slender, giving him a scholarly air rather than the air of a military man.
During the Morpho Elimination, Ernst wore the standard Federacy panzer jacket uniform, his shoulders adorned with unique rank slides that denoted his position as the commander-in-chief of the Federacy.
Ernst is a staunch idealist in upholding the goodwill of humanity, believing that mankind should rather go extinct if it has to get rid of those alien to them, especially children. He is often likened to a fire-breathing dragon, steadfast in protecting his ideals and willing to destroy anything, even mankind, if his ideals of a benevolent humanity are not achieved.
However, that is only his presidential persona. At home, he is laid back old man trying to play the role of a father. In his own words, he is attempting to compensate for a family he had lost, first by adopting Frederica and employing Teresa, then later adopting the survivors of Spearhead.
Ernst upbringing is largely unknown, however at some point in time he was married and had a family. Ernst was also a general of the Giadian Empire, however, he became disillusioned by its policies and as a result, he led a revolution that toppled the empire. During the tail end of the Siege of Rosenfort, Ernst faked the death of Augusta Frederica Adel-Adler, the last surviving member of the Giadian monarchy, and took her under his care. He then became the first and interim president of the newly formed Federal Republic of Giad.
As a former general of the Giadian Empire as well as the president of the Federacy, he has shown remarkable leadership skills as well as being able to inspire and intimidate anyone who is under him.
Ernst is Frederica's legal guardian. He faked her death following the end of the revolution and adopted her as his daughter. Frederica doesn't really see him as much of a father, referring to him as a mere paper pusher and a lowly bureaucrat. Nevertheless, she respects him as the head of government, believing that his revolution was necessary. Ernst also does not shy away to scold her if she’s being rude when she asked about Shin’s scar as well as punishing her for sneaking away to the battlefield with Nordlicht Squadron. However, Ernst always makes sure that his punishments will teach her well, as she had to do her arithmetic drills.
Teresa is Ernst's maid, taking care of the house and Frederica while Ernst is away. She is the spitting image of Ernst's wife, implying they may be sisters. Despite that, Ernst notes that he does not feel any attraction towards her.
"'Come back alive, All of you'" ― -Ernst Zimmerman to his adopted sons and daughters of Spearhead squadron as they embark to the battlefield
"'Attention, comrades! The Western Theatre Forces will begin an all-out march into Legion-held territory. This battle will determine not only the fate of the Federal Republic of Giad, but also those of the United Kingdom of Roa Gracia, the Alliance of Wald, and the other nations whose cries for help we haven't even heard yet! This is the greatest operation in the history of mankind. You are the mighty shield that defends your homeland, and the sharp sword that cuts open a future for humanity! We will be a symbol of justice for the world! Keep our successful battles close to your heart and advance, bravely, valiantly!'" ― To his troops during the MORPHO Elimination operation[source]
"'You allowed me to become President, and now you must live with the consequences! if you insist the only way we can survive is an unethical one, then you’ll have to die here along with my ideals.'" ― To his military staff, when an officer suggested to abandoned the soldiers sent in enemy territory after they’ve lost contact with them