 Cleven worked at the Columbia Hospital in New York City between 1893 and 1899; during this time, he studied music with Professor Brunker, who was also a personal friend of Cleven and also noted within the Norwegian community.Cleven became a maestro at violin and was active at boxing and wrestling and also became a personal acquaintance of the boxer Bob Fitzsimmons.In 1899, Cleven enlisted in the US Army during the Spanish–American War and was stationed in the Philippines as part of the 203rd New York Volunteer Infantry, eventually being promoted to sergeant in the US Army Musical Corps.