Kevin Hagen is the son of professional ballroom dancers, Haakon Olaf Hagen and Marvel Lucile Wadsworth. His father left the family when Kevin was five. He was raised by his mother, two aunts and a grandmother, with some help from his uncle, a physician. The family moved to Portland, Oregon when Kevin was a teenager and he played baseball and football at Jefferson High School. He attended Oregon State University before enlisting in the U.S. Navy after World War II, and served in San Diego.

At age 15, he weighed 250 pounds, but lost 60 pounds by the following summer.

His son, Kristopher Hagen (age 34 in 2005), is a Special Ed teacher and high school baseball coach in Bakersfield, California.

He was a single parent for some 20 years. He has been married four times.