 These prepaid plans burgeoned during the Great Depression as a method for providers to ensure constant and steady revenue.In 1970, the number of HMOs declined to fewer than 40.Paul M. Ellwood, Jr., often called the "father" of the HMO, began having discussions with what is today the U.S. Department of Health and Human Services that led to the enactment of the Health Maintenance Organization Act of 1973.