Aidan Gillen
Dr. Allen Hynek (20 eps)
Michael Malarkey
Captain Michael Quinn (20 eps)
Laura Mennell
Mimi Hynek (20 eps)
Ksenia Solo
Susie Miller (20 eps)
Neal McDonough
General James Harding (20 eps)
Michael Harney
General Hugh Valentine (20 eps)
Nicholas Holmes
Joel Hynek (12 eps)
Jill Morrison
Faye (11 eps)
Deborah Trotchine
Student (10 eps)
Ian Tracey
The Fixer (10 eps)
Robert John Burke
William Fairchild (7 eps)
Matt O'Leary
Lieutenant Henry Fuller (6 eps)
Jerod Haynes
Daniel Banks (5 eps)
Currie Graham
Cal Miller (5 eps)
Keir O'Donnell
Evan Blake (4 eps)
Michael Imperioli
Edward Rizzuto (3 eps)
Caspar Phillipson
John F. Kennedy (3 eps)
Sofia Milos
Daria (3 eps)
Heather Doerksen
Donna Smith (3 eps)
Zach McGowan
Duncan Booker (2 eps)
Spencer Garrett
General Ryan Blackstone (2 eps)
Bob Gunton
President Harry S. Truman (1 eps)
Thomas Kretschmann
Wernher von Braun (1 eps)
Bronson Pinchot
David Dubrovsky (1 eps)
Nolan Hupp
Eric (1 eps)
Jason Burkart
Greg (1 eps)
Christopher Heyerdahl
Edmund (1 eps)
Graham Greene
David (1 eps)