He was sometimes credited as "Don Arr". Christensen was a graduate of the Minnesota School of Art in Minneapolis. After finishing school he worked for the Walt Disney Studio from 1937 to 1941.
Christensen then worked briefly at Warner Brothers studio, primarily as a storyboard artist for Bob Clampett"s animation unit
After leaving Warner Brothers he worked independently for nearly four decades as a storyboard writer and artist, primarily for Western Publishing, Dell and Gold Key comic books, as well as Hanna Barbera, Walter Lantz Productions, DePatie-Freleng Enterprises, and other cartoon studios. He was involved with the Southern California Comic Artist Professionals Society for many years, and was a past President of the Comic Art Professional Society (CAPS).
Christensen died in Las Vegas, Nevada on October 18, 2006, at the age of 90 of natural causes. He beat the odds that he would not survive past 40, having been a Type I diabetic since the age of 13.