After World War II, LIFE magazine assigned staff photographer W. Eugene Smith to a human interest story about a doctor in Kremmling, Colorado. The story spanned 11 pages in LIFE’s September 20, 1948, edition. LIFE later summarized: “Country Doctor was an instant classic when published, establishing Smith as a master of the commanding young art form of the photo essay, and solidifying his stature as one of the most passionate and influential photojournalists of the 20th century.” This image depicts Dr. Ernest Ceriani making his rounds, as the only doctor within 400 miles of the 2000 residents of Kremmling. TIME magazine selected it as one of the 100 most influential photographs: “By digging so deeply into his assignment, Smith created a singular, starkly intimate glimpse into the life of a remarkable man. It became not only the most influential photo essay in history but the aspirational template for the form.”