Pan Am provided the requirements to Boeing for the 747. The cargo variant of the 747 was almost an afterthought. Source: https://www.barnesandnoble.com/w/747-

Pan Am provided the requirements to Boeing for the 747. The cargo variant of the 747 was almost an afterthought. Source: https://www.barnesandnoble.com/w/747-joe-sutter/1111077661 https://www.barnesandnoble.com/w/747-joe-sutter/1111077661