Gerhart is large, imposing man with a well built frame and thick black hair and moustache. He is an older man with wind-blown dark hair, mutton chops, tiny moustache, and light violet eyes. He wears a suit of dark gray with gold accents, and sports an elegant gold chain that hangs from his collar and buttons. A pinstriped vest of brown and tan can be seen under his lapel. He wears the colors of House Rogner, black and gold, with a purple trim on the bottom of his suit and shoes. His two piece suit is decorated with golden epaulettes and chains and is worn above a purple waistcoat and white cravat.
Gerhart is a prideful noble, quick to act whenever the Noble Faction is in need of his assistance, especially with the Reinford Group as Erebonia's foremost producer of weaponry based in his marquisdom. he shows a much more cooperative side after the war, and seems to relent his decisions, making peace with his contrasting daughter's perspective.
Rogner is head of one of the Four Great Houses, and believes himself to be a man of principle. He chafes at his daughter's rebelliousness and refusal to look and behave like a traditional noblewoman. It is later revealed that he has a certain pride, being stubborn to the point that he will only admit defeat when forced to yield. Still, he is a man of his word and expects fairness in all dealings. Gerhart admits that his stubborn personality is one quality he shares with his daughter.
After his daughter assisted Class VII to stop the Imperial Liberation Front in the Sachsen Iron Mine in Trails of Cold Steel, Chapter 6: "Progressive Chaos", he forced her to leave the Thors Military Academy. He agreed to let her visit the academy festival in order to meet a few prospective candidates for an arranged marriage proposal. He also forced her to wear a dress.
Although a supporter of the Noble Faction, Gerhart is not obsessed over his status as a noble compared to the duke of Cayenne and Albarea. Aside from his hostile attitude toward Chancellor Giliath Osborne's Reformist Faction, he is loyal to the imperial family. He also felt guilty over the Noble Alliance's decision to confine them to house arrest during the Erebonian Civil War.
In Trails of Cold Steel II, Act 2: "The Awakening Lions", after Class VII re-takes the Reinford building during the civil war and head their way toward the Schwarz Drache Barrier, Gerhart challenges his daughter to a duel in their Panzer Soldats. He initially has the upperhand, but Angelica parries his decisive attack using a Taito technique and sent Gerhart's Hector flying. She reminds him of a lesson he taught her, "true Erebonian nobles must always be able to stand on their two feet", and Gerhart admits defeat.
Afterwards, Gerhart declares his neutrality in the war, siding with neither Noble nor Reformist Faction. After the war, he interrogates Duke Cayenne and Duke Albarea alongside Rufus Albarea and Marquis Hyarms.
Although not seen in person, Gerhart is mentioned as declining to come to the noble summit in Ordis. He is mentioned as coming to Heimdallr following the disappearance of his daughter, but is also mentioned as having gone missing.