Due to page length, this page has been split into the following.
Spoiler warning: Trope titles are not marked as spoilers in this entry. Because of this, the trope listings spoil some events of the plot. If you are not caught up with the latest episodes and you do not wish to be spoiled, do not read past the description of each character, and do not open the Project Castor page if you have not watched up through at least 2x10.
- The Clones of Project LEDAnote Sarah Manning, Beth Childs, Alison Hendrix, Cosima Niehaus, Katja Obinger, Helena, Rachel Duncan, Jennifer Fitzsimmons, Tony Sawicki, Charlotte Bowles, Krystal Goderich, M.K., Miriam Johnson, Camila Torres, European clones, Helsinki clones, Vivi Valdez
- Associates of the Clonesnote Felix Dawkins, Vic Schmidt, Siobhan Sadler, Kira Manning, Amelia, Cal Morrison, Benjamin Kertland, Kendall Malone, Adele, Art Bell, Paul Dierden, Angela Deangelis, Toronto Police Department, Donnie Hendrix, Gemma and Oscar Hendrix, Aynsley Norris, Jason Kellerman, Marci Coates, Connie Hendrix, Alison's Neighbors, Delphine Cormier, Scott Smith, Shay Davydov, Hell Wizard, Jesse, Pupok
- The Proletheansnote Maggie Chen, Tomas, Hank Johanssen, Bonnie Johanssen, Gracie Johanssen, Alexis
- The Neolutionistsnote Dr. Aldous Leekie, Olivier Duval, Astrid, Dr. Virginia Coady, Trina, Frank and Roxie, Evie Cho, Marty Duko, The Board of Neolution, P.T. Westmoreland
- Dyad Associatesnote Andrew Peckham, Susan Duncan, Daniel Rosen, Marian Bowles, Dr. Alan Nealon, Ferdinand Chevalier, Bulldog
- The Clones of Project CASTORnote Mark Rollins, Styles Miller, Rudy, Seth, Parsons, Abel Johanssen, Ira Blair
- Miscellaneous Charactersnote Bobby, Colin, Ramon, Yvonne, Barry and Brenda, Willard Finch, David Benchman