Main •
Aidan Gillen as
Dr. J. Allen Hynek, an
astronomer,
astrophysicist, professor, and
UFOlogist working on Project Blue Book. The character is inspired by USAF Captain
Edward J. Ruppelt, the first director of the real-life Project Blue Book. •
Laura Mennell as Mimi Hynek, Allen Hynek's wife. •
Ksenia Solo as Susie Miller, a friend and neighbour of Mimi Hynek, also a
KGB agent. •
Michael Harney as General Hugh Valentine, a high-ranking military official, and founder of Project Blue Book. The character is inspired by USAF Brigadier General William Garland, a member of General
Charles P. Cabell staff during the time period of the real-life Project Blue Book.
Recurring •
Robert John Burke as William Fairchild, United States
Secretary of Defense. •
Ian Tracey as "The Fixer" a.k.a. "The Man in the Hat" (later revealed to be one of the
Men In Black), a mysterious man who follows Dr. Hynek. The character is partly inspired by
Ingo Swann, allegedly involved in the
Stargate Project. •
Matt O'Leary as Lieutenant Henry Fuller, a USAF pilot whom Hynek and Quinn meet on their first case. • Nicholas Holmes as
Joel Hynek, Mimi and Allen's son. •
Currie Graham as Susie’s Associate, also a KGB agent. • Jill Morrison as Faye, a member of the Air Force and Captain Quinn's secretary at Wright Patterson Air Force Base. •
Michael Imperioli as Edward Rizzuto, an American/Russian double agent.
Historical figures •
Adam Greydon Reid as
Donald Keyhoe (spelled in the credits as "Kehoe"), an American writer and UFO researcher. Keyhoe was widely regarded as the leader in the field of UFOlogy in the 1950s and early to mid-1960s, appearing in the episode entitled "The Lubbock Lights". •
Thomas Kretschmann as
Wernher von Braun, a German-American aerospace engineer. Von Braun was the leading figure in the development of rocket technology in Nazi Germany, before coming to the U.S. to develop rockets for
NASA, appearing in "Operation Paperclip". •
Bob Gunton as President
Harry S. Truman, 33rd President of the United States, appearing in "The Washington Merry-Go Round". •
Caspar Phillipson as Senator
John F. Kennedy, appearing in Season 2. Phillipson reprises his role from the 2016
biographical drama film Jackie and its 2017
spin-off short film The Speech JFK Never Gave, later reprising the role again in the 2022
biographical fiction film Blonde, in which he had portrayed an older Kennedy as the
President of the United States. ==Episodes==