Information from UFOSeries.com. With thanks to Marc Martin.

Ed BishopCommander Edward "Ed" Straker is a former American Air Force Colonel, pilot and astronaut originally from Boston, Massachusetts, who organised S.H.A.D.O. following a series of UFO attacks in 1970. Commander Straker's rank is Commander-in-Chief of S.H.A.D.O. Operations. Ed Straker also masquerades as the head of Harlington-Straker Film Studios, S.H.A.D.O. Headquarters being located directly below the film studio.


George SewellColonel Alec Freeman a former pilot and intelligence officer, is S.H.A.D.O.'s first officer (and very first operative recruited into S.H.A.D.O. by Commander Straker) for 17 episodes in the series (George Sewell left the show following the change of studios, being later unavailable when series production resumed at Pinewood Studios). Colonel Freeman is Commander Straker's closest friend and right-hand man and, occasionally, his muscle.17
Michael BillingtonColonel Paul Foster is introduced in the second episode, "Exposed". A former test pilot, his plane was critically damaged when S.H.A.D.O.'s Sky One intercepted and destroyed a UFO in close proximity to Paul Foster's jet. His persistent investigation of the incident threatened to expose S.H.A.D.O.'s existence, so Ed Straker offers him a position with S.H.A.D.O.21
Gabrielle DrakeLieutenant Gay Ellis, seen as Moonbase commander during the first half of the series. Lt. Ellis is occasionally portrayed as lacking self-confidence, and at other times as a take-charge officer. She is briefly reassigned to S.H.A.D.O. HQ when it is suggested that she may be romantically involved with interceptor pilot Mark Bradley ("Computer Affair"). She also appears to be attracted to Ed Straker, though nothing comes of this.10
Grant TaylorGeneral. James L. Henderson, Commander Straker's superior officer, serves as the president of the International Astrophysical Commission, which is a front for S.H.A.D.O. and is responsible for obtaining funds and equipment from various governments to keep S.H.A.D.O. perational. Straker and Henderson clash frequently over the needs of S.H.A.D.O. and economic realities.9
Wanda VenthamColonel Virginia Lake first appears in the opening episode of the series ("Identified"), as a S.H.A.D.O. engineer and scientist. A computer specialist, she was a member of the "Utronics" tracking device design team. During the last eight episodes Lake returned to take over the post of S.H.A.D.O. first officer, replacing Freeman. 9
Peter GordenaCaptain. Peter Carlin, during the first third of the series, Captain Carlin is the commander of the submarine Skydiver and pilot of its interceptor aircraft, Sky One. In 1970, Carlin and his sister found a UFO and were attacked; he was shot and wounded and his sister vanished. He joined S.H.A.D.O. in hopes of finding out what happened to his sister, and eventually learned that her organs had been harvested in pilot episode "Identified".6
Dolores MantezLieutenant Nina Barry is one of Straker's first recruits into S.H.A.D.O. Nina Barry works as a space tracker at Moonbase and later replaces Lt. Ellis as its commanding officer. She also serves aboard Skydiver at one point ("Sub-Smash").23
Gary MyersCaptain Lew Waterman was initially an interceptor pilot on the Moon but is later promoted to captain and replaces Peter Carlin as commanding officer of Skydiver and pilot of Sky One.13
Keith AlexanderLieutenant Keith Ford is a former television interviewer who became a founding member of S.H.A.D.O. and its main communications officer. Actor Keith Alexander left the series after the production break, so the character disappears at the two-thirds mark of the series.16
Ayshea BroughAyshea Johnson a S.H.A.D.O. headquarters officer in 14 episodes and later becomes S.H.A.D.O.'s communications officer following the departure of Lt. Ford.17
Vladek SheybalDoctor Douglas Jackson is the S.H.A.D.O. psychiatrist and science officer. He serves a number of capacities within S.H.A.D.O., including acting as prosecution officer during the court martial of Paul Foster. It is implied that "Douglas Jackson" is not the character's birth name, as he speaks with a strong Eastern European accent.14
Antonia EllisLieutenant Joan Harrington another Moonbase operative, was one of the organisation's earliest recruits, as seen in "Confetti Check A-O.K.".14
Norma RonaldMiss Ealand is a S.H.A.D.O. operative who masquerades as Ed Straker's movie studio secretary. She is the first line of defence against anyone entering S.H.A.D.O. HQ via Straker's office/elevator. The character is not seen in most of the post-studio change episodes, being replaced in two episodes by a Miss Holland, played by Lois Maxwell.11
Harry BairdLieutenant Mark Bradley is an Moonbase Interceptor pilot based on the Moon. He becomes romantically involved with Lt. Ellis for a time, leading to a temporary assignment at S.H.A.D.O. HQ on Earth, and later briefly assumes the position of Moonbase commander. Harry Baird left the series after filming four episodes, but appeared in stock footage in two later episodes.6