Karr's forces transformed much of Voyager into a holodeck, so that he could hunt the crew in holographic simulations of many historical eras and planets, including Earth's World War II and Klingon battles. Karr, in the Nazi simulation, wore the uniform of a Standartenführer, equivalent to a colonel. Some of the Hirogen under his command wanted to kill the crew and move on. He believed that the hunt had consumed the Hirogen and that their race was dying out because of the hunt. With a holodeck, they could keep the hunt tradition without having to spread all over the quadrant to do it and devote more time to maintaining their culture.
After Kathryn Janeway became aware of the situation, and the holodeck emitters started to fail causing the safety controls to go off line which resulted in bloody fighting on the ship, she and Karr agreed to a cease fire. She agreed to trade the holodeck technology in exchange for her ship and crew back. However, the Beta Hirogen, Turanj, refused to obey Karr's command and killed him. After a truce was declared, Janeway gave the departing Hirogen an optronic data core to create holographic technology on their own vessels, something she did so as to keep her word to Karr even after his death. (VOY: "The Killing Game", "The Killing Game, Part II")