Although born in Nebraska, Dan Sullivan grew up in Montana. He was able to compete at the 1906 Olympics only at the last minute when funds were raised for his trip. Sullivan was one of five athletic brothers, Jack, Gene, Phil, Gerry, and Dan. Dan was known as Montana Dan, in contrast to his brother, Montana Jack. Both of them became professional boxers, although Montana Dan’s career was not a stellar one. He fought as a pro from 1909-18, although there is a recorded bout for him in 1904, before his Olympic appearance. Sullivan’s professional record was 7 wins, 15 losses, and 3 draws. After that career ended, he had somewhat of an itinerant life, living in Boston for several years. Later in life, he worked as a timekeeper at the High Ore Mine for the Anaconda Company, back in Montana, where he died.