Karl Eller was born in Chicago on June 20, 1928. At the age of nine, Eller and his family moved to Tucson, where he attended Tucson High School and was a two-sport athlete in football and basketball, winning a football state championship in 1945. After graduating in 1946, Eller served three years in the Army, including two years in Japan.
Following his military service, Eller enrolled at the University of Arizona. There, he met his wife, Joan Stevens. Shortly after the couple graduated from the university, Eller began his career in advertising, working for the New York-based Foster & Kleiser.
Bill Shover recruited Eller specifically for his network television contacts — an asset that proved invaluable when pitching a new bowl game to the NCAA and major networks. Eller joined the executive committee as a founding member in 1971. Seven years later, he played an instrumental role in expanding the Pac-8 Conference by adding both ASU and the University of Arizona.
In 1959, Eller began working for the Needham, Louis and Brody advertising agency in Chicago where his most notable achievement was creating miniature candy bars for Mars, Incorporated. Eller worked for three years at the Chicago-based firm before moving back to Arizona in 1962. Upon his return to the state, he purchased the Arizona branch of Foster & Kleiser and renamed it Eller Outdoor Advertising. After purchasing several newspapers, television and radio stations, the outdoor advertising company evolved into Combined Communications.
Eller was heavily invested in the formation of two Phoenix professional sports teams: the WHL's Phoenix Roadrunners, founded in 1967, and the NBA's Phoenix Suns, founded in 1968. In 1968, he was also named one of three investors in the Suns.
In 1971, Eller joined the eight other founders who brought the Fiesta Bowl to Arizona and became instrumental in expanding the PAC-8 Conference, later known as the Pac-12 Conference, by adding both Arizona State University and the University of Arizona. In the 1980s, Eller became the CEO of Circle K and expanded their operations to the second-largest convenience store chain in the country. In 1992, Eller purchased Gannett's Billboard business. Within five years, it became one of the largest media companies in the U.S. He would sell the business in 1997 for $1.5 billion.
Eller officially retired in 2001 but remained active within the University of Arizona's Board of Trustees. On March 10, 2019, Eller passed away. His legacy lives on through achievements like the Fiesta Bowl, Mars mini candy bars and the University of Arizona's Eller College of Management.