Born in Parral, Chihuahua on July 17, 1905, son of James E. Hyslop and Maria Beckmann, Guillermo came from an influential family, well known in Mexico. Guillermo spent his childhood in the city of Parral, Chihuahua , where he lived with two brothers and four sisters. At the age of 15 years Guillermo moved to El Paso, Texas, where he completed his high school studies.
