Abstract: Probably most readers will have heard of the OODA (Observation-Orientation-Decision-Action) loop or 'Boyd Cycle' as a concept to describe the sequence of decision and action within military operations. Some will probably be aware that this concept was developed by John Boyd, a United States Air Force officer, to explain his finding that the USAF's less manoeuvrable and slower climbing F86 Sabre fighter aircraft still managed to consistently defeat Chinese Mig 15s during air-to-air combat over Korea. Yet few will know enough of the life, career and thoughts of John Boyd to assess his place as a military thinker and strategist of the 20th century. Colin S. Gray, the strategic theorist, leaves no doubt of his assessment when he describes Boyd's work as able to: '... apply to the operational, strategic, and political levels of war, as well as to tactics for aerial dogfights. Boyd's theory claims that the key to success in conflict is to operate inside the opponent's decision cycle. ... The OODA loop may appear too humble to merit categorization as a grand theory, but that is what it is. It has an elegant simplicity, an extensive domain of applicability, and contains a high quality of insight about strategic essentials, such that its author well merits honourable mention as an outstanding general theorist of strategy.'