UFO had a large ensemble cast; many of its members would come and go during the course of the series, with a number of actors — most notably George Sewell and Gabrielle Drake — leaving midway through the series, during the production break necessitated by the change of studios. It is established early on that S.H.A.D.O. personnel rotate between positions, so the occasional disappearance of characters — some of whom would later return in other positions — fits in with the concept of the series. Also, owing to the scheduling of the series not reflecting the production order, some episodes featuring departed cast members were not broadcast until later in the series, which can give the impression that no major cast changes occurred.

NB: Only Ed Bishop (Commander Ed Straker) appeared in every episode of UFO.

ACTORUFO CharacterAbout this characterNo. of Episodes
Ed BishopCommander Ed Straker, Cmdr-in-chief of S.H.A.D.O.Commander 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. Ed Straker masquerades as the head of Harlington-Straker Film Studios, S.H.A.D.O. Headquarters is located 80ft directly below the film studios.26
Dolores MantezLieutenant Nina Barry, Moonbase OperativeLieutenant Nina Barry is one of Straker's first recruits into S.H.A.D.O. Lt. Barry works as a space tracker at Moonbase and later replaces Lt. Gay Ellis as its commanding officer. She also serves aboard Skydiver in the UFO Episode, "Sub-Smash".23
Michael BillingtonColonel Paul Foster, S.H.A.D.O. OperativeColonel 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 Foster's jet. Foster's persistent investigation of the incident threatened to expose S.H.A.D.O.'s existence, so Straker offers him a position with S.H.A.D.O.21
George SewellColonel Alec Freeman, Second-in-command S.H.A.D.O.Colonel Alec E. Freeman, 2nd-in-command of S.H.A.D.O. 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 Straker) for 17 episodes in the series. Freeman is Straker's closest friend and right-hand man and, occasionally, his muscle. George Sewell left following the change of studios, being later unavailable when series production resumed at Pinewood Studios.17
Ayshea BroughLieutenant Ayshea Johnson, S.H.A.D.O. headquarters officerLieutenant Ayshea Johnson is a S.H.A.D.O. headquarters officer, and later becomes S.H.A.D.O.'s communications officer following the departure of Lt. Ford.17
Keith AlexanderLt. Keith Ford, Communications OfficerLieutenant 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
Vladek SheybalDr. Douglas Jackson, S.H.A.D.O. Medical OfficerDr. 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 EllisSpace Tracker Joan Harrington, Moonbase operativeSpace Tracker Joan Harrington is another Moonbase operative, and was one of the S.H.A.D.O. organisation's earliest recruits, as seen in "Confetti Check A-O.K.".14
Gary MyersCaptain Lew Waterman, 2nd Commander of SkydiverCaptain Lew Waterman is initially an interceptor pilot on the Moon; he is later promoted to Captain, and replaces Peter Carlin as commanding officer of Skydiver and pilot of Sky One.13
Norma RonaldMiss Ealand, Ed Straker's Personal SecretaryMiss Ealand is a S.H.A.D.O. operative who masquerades as Straker's movie studio secretary. Miss Ealand is the first line of defence against anyone entering S.H.A.D.O. HQ via Commander Straker's office/elevator. Her character is not seen in most of the post-studio change episodes, as she was pregnant during the production break and latter half of the making of UFO and missed some episodes such as 'The Cat With Ten Lives' and 'The Man Who Came Back'. Norma was replaced by Lois Maxwell – Miss Moneypenny from the James Bond films. However, some dialogue with “Miss Holland” (where Ed Straker tells her he’ll wait for Miss Ealand to read a movie script when she returns) suggests that Miss Ealand also helped maintain Ed Straker’s secret identity as a movie boss.11
Gabrielle DrakeLieutenant Gay Ellis, Moonbase CommanderLieutenant 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".10
Grant TaylorGeneral James Henderson, President of I.A.C.General James L. Henderson, President of IAC (International Astrophysical Commission), Straker's superior officer. The I.A.C. 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. Straker and Henderson clash frequently over the needs of S.H.A.D.O. and economic realities.9
Wanda VenthamColonel Virginia Lake, S.H.A.D.O. OperativeColonel Virginia Lake first appears in the opening episode of the series "Identified", as a S.H.A.D.O. scientist. A computer specialist, she was a member of the design team for the "Eutronics" tracking device. During the last eight episodes, Lake returned to take over the post of S.H.A.D.O. first officer, replacing Freeman.9
Peter GordenoCaptain Peter Carlin, first commander of SkydiverCapt. Peter Carlin, during the first third of the series, 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 the hope of finding out what happened to his sister, and eventually learned that her organs had been harvested in the pilot episode "Identified".6
Harry BairdLieutenant Mark Bradley, interceptor pilotLieutenant Mark Bradley is a Caribbean-born interceptor pilot based on the Moon. He becomes romantically involved with Lieutenant 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
Other characters
Minor characters : One of the female Moonbase operatives, Joanna, was played by Shakira Baksh, who later married actor Michael Caine. Producer Gerry Anderson later said that he had lost his temper with her so badly on the set of UFO that he always feared the idea of running into Michael Caine at some actors' function, and being punched on the nose by him.

Steve Minto, one of the Interceptor pilots, was played by the actor Steven Berkoff.

Lieutenant Sylvia Howell, a Skydiver technician, was played by the actress Georgina Moon.