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 80ft directly below the film studios.


George SewellColonel Alec E. Freeman a former pilot and intelligence officer. He 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 J. 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 within S.H.A.D.O.21
Gabrielle DrakeLieutenant Gay Ellis is 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 is 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. operational. Commander Straker and General Henderson frequently clash 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 scientist, chief designer and engineer at Westbrook Electronics in Los Angeles. A computer specialist, she is chief designer of the "Utronics" tracking device design team. During the last eight episodes Colonel Lake returned to take over the post of S.H.A.D.O. first officer, replacing Col. Freeman.9
Peter GordenoCaptain. Peter Carlin: during the first third of the series, Captain Carlin is the commander of 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 the hopes of finding out what happened to his sister, and eventually learned that her organs had been harvested at the end of the 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".17
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 is a S.H.A.D.O. headquarters operative in 14 UFO episodes and later becomes S.H.A.D.O.'s communications officer following the departure/transfer of Lt. Ford.17
Vladek SheybalDoctor Doug 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 Executive Secretary at the Harlington-Straker Film Studios. However, Miss Ealand is actually a S.H.A.D.O. operative who merely masquerades as Ed Straker's movie studio secretary. Miss Ealand is the first line of defence against anyone entering S.H.A.D.O. Headquarters via Ed Straker's office/elevator.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 reassignment at S.H.A.D.O. HQ on Earth, and later briefly assumes the position of Moonbase Commander when Col. Paul Foster is believed to have been killed. Harry Baird left the series after filming four episodes, but appeared in stock footage in two later episodes.6