Mullen High School was named for John Kernan Mullen, businessman, philanthropist, and founder of the Colorado Milling and Elevator Company. Together with his wife, Catherine, Mullen envisioned the founding of a high school in Denver for orphaned boys. In 1928, working with Henry Tihen, Mullen contacted Edward Flanagan, the founder of Boys Town, for advice on how best to design and operate such a school. Following Flanagan's recommendation, Mullen wrote to the Christian Brothers of St. John Baptist de La Salle in Santa Fe, New Mexico, and invited them to be the directors and teachers of his planned school.