Duur was a Capellan warrior of Capella IV. He had previously met Federation Doctor Leonard McCoy during his visit to Capella IV sometime prior to 2267.

A close female relative of his was sent into the tent where Kirk, Spock and McCoy were held captive. She offered a plate of fruit to Kirk, however, McCoy warned him, that touching it would mean that Durr must challenge him to death. When Duur arrived to the tent, he discovered that Kirk did not accept his challenge, the disappointed Capellan responded with just one word: "Chur-ah."

He was a member of one of the Ten Tribes that became embroiled in a power struggle after the murder of the Teer. After being incapacitated by a rock slide caused by Kirk and Spock, he was killed by Kras with his own sword, in order to retrieve the type 1 phaser that Duur was carrying. (TOS: "Friday's Child")

Duur was played by actor Kirk Raymone.