He was a member of the Nazi party who was in charge of a province in France. He showed interest in the Brigitte character, who B'Elanna Torres was playing, and eventually had impregnated her.
A brutal man and very much believing in Adolf Hitler's ideals that Germans are the "master race" and having "pure blood", causing Karr to criticize him for "underestimating his prey". He eventually persuaded Karr to ignore his Alpha's orders after the Hirogen and Voyager's crew agreed to a cease fire.
The script notes describe him as "an attractive young German Officer we'll call Kapitan"; it also noted he had "a light German accent." The call sheets also listed him as "Kapitan".
Though not referenced on-screen, the producers usee a misnomer in choosing the term "Kapitän"; where Kapitän (with the "zur See" [at sea] suffix) actually refers to a naval captain in both the Kriegsmarine, the German navy, as well as its merchant marine. Since he was an SS officer, the correct rank, based on his rank insignia would have been hauptsturmführer, however, he was ultimately called "hauptmann" on-screen, which was actually the regular German Army equivalence of the rank.
Le Coeur de Lion patrons
These holographic Humans were part of the Sainte Claire holoprogram. They visited "Le Coeur de Lion" and listened to Mademoiselle de Neuf. Every guest was welcomed by Katrine and told to leave the war outside. Jacques was one of the patrons. (VOY: "The Killing Game")
These Nazi officers were part of the World War II scenario recreated aboard Voyager by the Hirogen. They visited Le Coeur de Lion and listened to Mademoiselle de Neuf's performance. Later, they were roaming the streets of Sainte Claire and assisted their leading officers in apprehending the characters played by Seven of Nine and Neelix.
These Nazi soldiers were part of the Hirogen takeover of Sainte Claire and took part in several firefights with the American soldiers and later the hand-to-hand combat with the Klingons. (VOY: "The Killing Game, Part II")
This character was played by recurring background actor Ken Gruz. For his appearance, the script stated, "[a] German Radio Operator (non-speaking) mans the radio, wearing a headset."
These two waiters were part of the World War II holoprogram aboard Voyager run by the Hirogen. Both were employed at Le Coeur de Lion and worked for Katrine while Mademoiselle de Neuf performed on stage. (VOY: "The Killing Game")