Arthur Michael (Jack) Hagan, geologist, was born to J. P. and Clara (Klingle) Hagan on September 25, 1892, in Jollytown, Pennsylvania. A talented baseball player, he attended St. Vincents College and the University of West Virginia on athletic scholarships. In 1918 he graduated from the university, where he studied under Dr. I. C. White, founder of the anticlinal folding theory, a theory Hagan believed in the whole of his professional life. Hagan served in the army during World War I and had reached the rank of sergeant when he was discharged. In 1919 he joined Transcontinental Oil Company as a geologist and worked under Ray V. Hennen. Hagan was sent to Mississippi, Louisiana, Tennessee, Colorado, Oklahoma, and then Texas. During 1921–22 he worked in Brazil and Venezuela and then returned to Texas. In 1923 he chose the sixteen sections that became the Big Lake oilfield for the Benedum-Trees organization to buy from the Texon Oil and Land Company; the same year he chose the location for the Transcontinental's discovery well in the Yates oilfield in Pecos County. Hagan left the company in 1926 and with John W. Emch opened a consulting geological and general oil operations firm in San Angelo. In 1929 Hagan moved to Corpus Christi, where he reentered the employ of Benedum-Trees but returned to San Angelo in 1942. In 1927 Hagan married Helen Frances Quinn, whose sister was the wife of Ray Hennen and who had also worked for Transcontinental. They had two children, A. M. Hagan, Jr., and Helen Patricia Hagan. Hagan was a Catholic, a member of the American Association of Petroleum Engineers, and a charter member of the San Angelo Geological Society. He died at his home on December 19, 1957. At the time of his death he had an office in the McBurnett Building in San Angelo and was an active consulting geologist. After his death, the San Angelo Geological Society dedicated its guidebook to him. With Hennen, he was inducted into the Permian Basin Petroleum Museum's Hall of Fame in October 1975.