Karl Martz was born June 24, 1912, in Columbus, Ohio. His father, Velorus Martz, was a high school principal there. Karl's mother, Amy Lee Kidwell Martz, was a talented woman who played the piano, did photography including her own processing and printing, sewed, gardened, canned, entertained, and was a loving mother to three successful children. She earned a degree in Home Economics at Ohio State University, and early in her life was a nutritional adviser to rural women. Karl's brother Robert was a career Air Force officer, after which he went into administration at Indiana University. Karl's sister Martha married Otto Grant, a lawyer in Fort Wayne, Indiana, and was a loving mother to four children.

Here is a photograph of Karl at age 8, with his family.

In 1925, Velorus became a faculty member in the School of Education at Indiana University, Bloomington, where he was well-regarded for over 25 years. Karl's education continued in Bloomington, where he went to Bloomington High School, and then to Indiana University, where he majored in Chemistry.