Steele started off as a Marine Corps infantry and intelligence officer. After four years on active duty, he joined the CIA for about a decade before co-founding the Marine Corps Intelligence Activity, where he was deputy director. Widely recognised as the leader of the Open Source Intelligence (OSINT) paradigm, Steele went on to write the handbooks on OSINT for NATO, the US Defense Intelligence Agency and the U.S. Special Operations Forces. In passing, he personally trained 7,500 officers from over 66 countries.