Dennis Kim was a Human male and a cousin of Harry Kim.
Harry and Dennis had a mutual friend, Maxwell Soroyan, who was killed by the Maquis a few years prior to 2377. When the USS Voyager reestablished communications with the Alpha Quadrant, Dennis wrote a letter to Harry in which he talked about Soroyan's death. (VOY: "Repression")
This character was only mentioned in dialogue.