Hugo W. Koehler was born on July 19, 1886, in St. Louis, Missouri, and named after a paternal uncle. His father, Oscar C. Koehler (1857–1902), was a first-generation German-American and second-generation St. Louis and Davenport, Iowa brewer and entrepreneur. Although it was privately rumored for much of his life that Hugo was the illegitimate son of Rudolf, Crown Prince of Austria, who is generally believed to have died with his teenage mistress, Baroness Mary Vetsera, in a murder-suicide pact in January 1889 (the "Mayerling incident"), no corroborating evidence of this ancestry has been established. The speculation was fueled by a few factors: 1) Koehler, who was reputed to be the "wealthiest officer" in the American navy in the 1920s, was apparently the beneficiary of a substantial trust fund. It was further speculated that this trust had been established by the Habsburgs with approval of the Holy See when Hugo Koehler was a child, to provide for his support and maintenance; 2) As a child, Hugo made several European visits with his paternal grandfather, Heinrich (Henry) Koehler, Sr.] (1828-1909), where he was introduced to aristocracy and elites; and 3) Koehler had the distinctive Habsburg chin.