Harry Marston Haldeman (5 April 1871 – 10 March 1930) was a significant business and social contact of L. Frank Baum.
Originally from Chicago like Baum, Haldeman was an owner and executive of plumbing companies in Los Angeles. Marston founded the Uplifters, the Los Angeles social club that was an important influence in Baum's life during his years in California. Baum composed the lyrics for the club's official song, which was titled "Haldeman."
H. M. Haldeman also served as the secretary of the Oz Film Manufacturing Company during its brief existence. He was credited as an executive producer on all four of the films the company made from Baum's works.
Haldeman was politically active, as a conservative Republican and an ardent opponent of Communism; he co-founded the Better America Foundation of California, an early anti-Communist organization. He was the grandfather of H. R. Haldeman, who gained national notoriety during the administration of President Richard Nixon.