| Set against the backdrop of the greatest clandestine race against time in the history of science with the mission to build the world's first atomic bomb in Los Alamos, New Mexico. Flawed scientists and their families attempt to co-exist in a world where secrets and lies infiltrate every aspect of their lives. |
| Name | Character | Episodes |
|---|---|---|
| Rachel Brosnahan | Abby Isaacs | 23 |
| Ashley Zukerman | Charlie Isaacs | 23 |
| Olivia Williams | Liza Winter | 23 |
| Harry Lloyd | Paul Crosley | 23 |
| Katja Herbers | Helen Prins | 23 |
| Michael Chernus | Louis "Fritz" Fedowitz | 23 |
| Christopher Denham | Jim Meeks | 23 |
| John Benjamin Hickey | Frank Winter | 23 |
| Daniel Stern | Glen Babbit | 13 |
| Alexia Fast | Callie Winter | 13 |
| Stafford Douglas | Thatcher | 11 |
| David Harbour | Reed Akley | 10 |
| William Petersen | Col. Emmett Darrow | 10 |
| Lauren Chavez-Myers | Jeannie | 9 |
| Richard Schiff | Occam | 8 |
| Travis Hammer | O'Byrne | 8 |
| Mark Moses | Col. Alden Cox | 8 |
| Daniel London | J. Robert Oppenheimer | 8 |
| Jefferson White | Cole 'Iowa' Dunlavey | 6 |
| Jason Ralph | Stan | 6 |
| Mamie Gummer | Nora | 6 |
| Peter Stormare | Lazar | 5 |
| Bill Camp | William Hogarth | 5 |
| Christina Kirk | Rose Akley | 5 |
| Audrey Moore | Francine | 5 |
| Griffin Dunne | Woodrow Lorentzen | 4 |
| Eddie Shin | Sid Liao | 4 |
| Carole Weyers | Elodie | 4 |
| Carole Weyers | Elodie Lancefield | 4 |
| Jefferson White | Cole | 3 |
| Adam Godley | Dr. Adelman | 3 |
| Josh Cooke | Lancefield | 3 |
| Jonny Coyne | Dr. Alek Barath | 3 |
| Ryan Jason Cook | Stanhope | 3 |
| Joanne Camp | Oppenheimer's Secretary | 3 |
| Neve Campbell | Kitty Oppenheimer | 2 |
| John Carroll Lynch | Daniel Ellis | 2 |
| Justin Kirk | Joseph Bucher | 2 |
| Josh Cooke | Tom Lancefield | 2 |
| Matthew Page | Weaver | 2 |
| Kenneth Miller | Purcell | 2 |
| Beth Bailey | Fay | 2 |
| Shylo Molina | Featured Child | 2 |
| Bruce McIntosh | Samaritan | 2 |
| Brad Garrett | Eli Isaacs | 1 |
| Gerald McRaney | Sec. Hentry Stimson | 1 |
| Jessica Hecht | Miriam Rubins | 1 |
| Robin Thomas | Maxwell Rubins | 1 |
| Glenn Morshower | Censorship Captain | 1 |
| Michael O'Neill | Psychiatrist | 1 |
| Christian Clemenson | Niels Bohr | 1 |
| Raoul Max Trujillo | Javier | 1 |
| Vic Browder | Deputy | 1 |
| Mark Sivertsen | Staff Sergeant | 1 |
| David Midthunder | Aniceto | 1 |
| Fiona Dourif | Jean Tatlock (voice) | 1 |
| Fiona Dourif | Jean Tatlock | 1 |
| Lora Martinez-Cunningham | Ida | 1 |
| Kevin Wiggins | Field Sergeant | 1 |
| Tony Devon | Omar | 1 |
| Matthew Page | Edgar | 1 |
| Kenneth Miller | Purcell / MP1 | 1 |
| Philip Ettinger | Watts | 1 |
| Debrianna Mansini | Dorothy | 1 |
| Kristen DeVore Rakes | Wilma | 1 |
| John Gabriel Rodriquez | Travis | 1 |
| Dave Racki | Soldier #1 | 1 |
| Sarah Minnich | Vera | 1 |
| Bryan Head | Soldier #2 | 1 |
| Genia Michaela | Ruth | 1 |
| Trine Christensen | Nurse | 1 |
| Frank Bond | Tupper | 1 |
| Joshua Rollins | Tuck | 1 |