The various characters affiliated in some way with Dyad.
- Played by: Matthew Bennett"Do one more thing to help her so I can put a bullet in your head."
An agent of Dyad sent to collect Sarah and Kira when they prove to be uncooperative.
- The Brute: He does Dyad's dirty work.
- Cold-Blooded Torture: On Sarah, despite having orders not to do so. Sadly for him, he gets interrupted by Helena.
- Implacable Man: Relentlessly pursues Sarah, even managing to survive a car accident involving the both of them. It takes the series' implacable woman, Helena, to take him down.
- Jerkass: Rarely even makes the effort to be polite.
- The Lost Lenore: Becomes one to Rachel after Helena kills him.
- Scarily Competent Tracker: No matter where Sarah goes, he's able to find her.
- Screw the Rules, I Have Connections!: He acts as ruthlessly as he does because Dyad will clean up whatever fallout results from his actions.
- Slashed Throat: How he is killed by Helena.
- Would Hit a Girl: Has no qualms about using physical violence against the clones, even when directly instructed not to.
Andrew Peckham/Ethan Duncan
- Played by: Andrew Gillies"Don't despair, my dear. Don't despair."
A man taking care of a lot of birds in a house crammed full of old papers. Actually Rachel's adoptive father, hiding from Aldous Leekie.
- Adult Fear: His wife was murdered in an arson attack (or so he thinks) and their daughter was kidnapped. He's spent the last two decades in hiding.
- Affectionate Nickname: Calls the LEDA clones his "little girls".
- Badass Boast: "I'm nobody's pawn."
- Cloud Cuckoolander: Appears to be this, what with his seeming obsession with his birds. 2.07 hints that this may be a case of Obfuscating Insanity, however.
- Crazy-Prepared: Gives Kira his old copy of The Island of Dr. Moreau which also happens to contain a significant amount of his notes including, it is implied, the key to the cipher for his work.
- Did Not Think This Through: The infertility sequence he added to the clones' DNA had the side effect of triggering a fatal autoimmune disorder. When he learns of this, he sets off to correct it.
- Disappeared Dad: Of Rachel. Would be played perfectly straight if his DNA played a part in the clones' creation.
- Driven to Suicide: He drinks poisoned tea to prevent Dyad from accessing any more of his work.
- For Science!: Was among the scientists who first created the clones, purely for scientific advancement, until the military took over.
- From Bad to Worse: First, the military became interested in the cloning experiment he and his wife were part of. Then, the Neolutionists took over the Dyad Institute, which eventually culminated in his wife getting killed and his adoptive daughter stolen from him. Presently, Leekie has been looking for him, presumably to kill him. And then he discovers his daughter is a sociopath and wants his research for unethical ends, which ultimately leads to his suicide.
- He Knows Too Much: Dyad targeted him and his wife because they threatened to go public with the clone experiment. Since the attempt on his life, he's been hiding out with the Birdwatchers.
- Heroic Suicide: He kills himself to prevent Rachel from abusing his knowledge.
- Nerves of Steel: He's hard to intimidate.
- Walking Spoiler: Due to his importance to both the plot and the backstory.
Susan Duncan (née Wakefield)
- Played by: Rosemary Dunsmore
Rachel's adoptive mother and co-creator of Project LEDA.
- Ambiguously Evil: See FaceHeel Turn below.
- Bullying a Dragon: It probably wasn't that bright of her to antagonise Rachel in the Season Four finale.
- Character Death: She's killed after getting caught trying to kill Westmoreland and buried in the Revival graveyard.
- FaceHeel Turn: According to what Ethan Duncan told Kendall Malone, Susan was "corrupted by Neolution". However, this is either subverted or at worst downplayed when it turns out she's been personally looking after the Leda clones' well-being and doing her best to protect them from others who mean them much worse. There is, however, also the matter of BrightBorn; it's not currently clear how involved she is with it or how much control she has over it. If she is in fact at all villainous, which is at this point not at all clear, she is certainly A Lighter Shade of Black and/or an Anti-Villain.
- For Science!: The reason she and her husband started the cloning project.
- Good Parents: Along with her husband Ethan, she was this for Rachel, as evidenced by Rachel's Happier Home Movie of her childhood.
- She Knows Too Much: The reason she and her husband were targeted by Dyad, because they threatened to go public with their clone experiments. He survived, but she didn't. Except she didn't die either.
- Killed Off for Real: Killed in a lab fire by Aldous Leakie before the series began. Except she's actually still alive and dies for real in Season 5.
- Kill It with Fire: Died in a lab fire caused by Aldous Leakie. Or so we were lead to think.
- Make It Look Like an Accident: Her death was ruled accidental, but it was actually due to an arson attack. Except it turns that she didn't die, either.
- Missing Mom: To Rachel.
- Not Quite Dead: She's revealed to be alive at the end of Season 3. And then she dies for real midway through Seaosn 5.
- Parental Incest: She's in a relationship with her adopted son Ira, a Castor clone.
- Posthumous Character: Except she isn't.
- Walking Spoiler: Hugely important to the backstory.
- Played by: Michelle Forbes"Like Siobhan, I'm invested."
One of Rachel's superiors at the Dyad Institute.
- Affably Evil: Assuming she is evil.
- Ambiguously Evil: It's hard to tell who she's loyal to or what she wants but she seems to be allying with Sarah.
- Bad Boss: We're told that she knew about and was possibly involved in the murder of Rachel's mother, but let Leekie take the fall for it. This later turns out to be false: Rachel's mother isn't even dead. It's not really clear what her angle was now, but since Charlotte shows up with Rachel's mother it's possible they're in it together somehow.
- Hidden Heart of Gold: As shady as she is, she appears to genuinely love her adopted daughter Charlotte and takes a huge risk to free Sarah and Kira from Dyad (though there's likely more to that than just good will).
- Manipulative Bastard: She's certainly good at manipulating people.
- The Mole: She has a high-ranking position in Dyad, but she has her own agenda unknown to the rest of the company. She is also possibly the only person in the company who knows about Project CASTOR.
- Only in It for the Money: Subverted. She'll freely admit that she likes the monetary gain that comes with her position, but she's motivated by much more than that.
- Smug Snake: She initially comes across this way, though she's later revealed to be quite a bit more competent than a typical example of the trope.
- Token Good Teammate: Possibly one for the Dyad institute. She helps Sarah and Kira escape.
- What Happened to the Mouse?: She disappears after the start of Season 3, although she's frequently mentioned. Considering that Charlotte shows up in the season finale claiming that Rachel is going to be her 'new mum' her fate isn't looking good. M.K. suggests that she is dead in Season Four, but it's still not clear what happened to her.
Dr. Alan Nealon
- Played by: Tom McCamus"Hard science requires hard choices."
A geneticist and researcher at the Dyad Institute who would be bring in doctors inside Paul's apartment to medically examine Beth, and later, Sarah, disguised as Beth, in their sleep. He formally introduces himself to Sarah in the second season finale.
- The Caretaker: To Rachel after her brain injury in Season 3.
- Early-Bird Cameo: He was one of the scientists examining Sarah in her sleep back when she was impersonating Beth.
- Omnidisciplinary Scientist: He's a geneticist, but also a surgeon as well, if him personally heading up Sarah's would-be oopherectomy is anything to go by. Later he performs eye-surgery on Rachel.
- Tuckerization: Dr. Nealon is named after one of the writers, Aubrey Nealon.
- Undying Loyalty: To Rachel. He kidnaps Krystal Goderitch and puts her in a medically-induced coma as a Body Double for Rachel, while Rachel escapes the Dyad Institute, having stolen Krystal's identity earlier in the episode.
- Subverted; he's a Neolutionist complicit in sending Rachel off to Susan Duncan.
- Played by: James Frain
Ferdinand is a well-educated, cool to the touch, charming, and intimidating cleaner. A powerful player in a secretive, multi-national cabal, he acts with questionable ethics and a ruthless modus operandi. His association with the Dyad Institute could mean big trouble for the Leda clones.
- All Women Are Doms, All Men Are Subs: What his sexual relationship with Rachel was like. And still is, as of the season four finale.
- Ambiguously Evil: He's on the clones' side for a while, but he's just as ruthless in his methods as ever. He could be interpreted as an Anti-Hero or as an Anti-Villain who happens to be allied with the heroes.
- Bastard Bastard: The illegitimate child of British aristocracy, according to Mika.
- Berserk Button: He hates Neolutionists, as he proves when he rants angrily about them while bludgeoning Bulldog to death with a baseball bat.
- Big Damn Heroes: He saves Sarah from a Dyad employee disguised as a dentist.
- Enemy Mine: Aligns himself with the clones after it's revealed that the Neolutionists were using him to acquire genetic material from the Castor/Leda original."This changes everything... which makes us new BFFs."
- Even Evil Has Loved Ones: "What can I say? Rachel pierced this armoured heart."
- Evil Brit: Starts out this way, seemingly.
- Evil Chef: He's a skilled foodie in the kitchen as well as a murdering psychopath.
- Four Eyes, Zero Soul: Initially is this at the start of Season 3, but is ultimately subverted in the Season 3 finale when his quirky side is revealed while dealing with Bulldog.
- Genre Savvy: It doesn't take long for Ferdinand to realize that he was being used by the Neolutionists. With Sarah's statement that Neolution wants Kendall's sample, he immediately suspects a mole, and (knowing that Sarah, Mrs. S, and Kendall aren't one) rapidly concludes that it is his associate, Bulldog. He also rapidly concludes that Sarah and Mrs. S had some way to dispose of dead bodies and immediately proceeds to use it on Bulldog.
- HeelFace Revolving Door: Allies with Leda in the season three finale, but seems to have aligned himself with Rachel, another occupant of the HeelFace Revolving Door, in the season four.
- Hyper-Awareness: He's very good at telling when something's off about a person or situation.
- Killed Off for Real: Manages to kill Mrs S in 5x08, but not before she takes him down with her.
- Meaningful Name: His surname "Chevalier" is French for "knight." Sure enough, he's very much Rachel's "knight."
- Mutual Kill: He and Mrs. S eventually shoot one another.
- No Sense of Personal Space: He gets very up close and personal with Sarah and Alison.
- Undying Loyalty: To Rachel. He's even willing to drop his hatred of Neolutionists for her... unfortunately for the rest of the clones.
- Played by: Earl Pastko
Ferdinands silent, imposing and violent personal bodyguard. Communicating with his boss by looks only, Bulldog carries out the dirty work of his shady employers.
- The Brute: For Ferdinand. In 3.01, he attempts to assassinate the Hendrix family until Ferdinand calls back the order.
- The Mole: One of the Neolutionists who infiltrated Dyad.
- Only Known by Their Nickname: His real name is never given.
- The Voiceless: Only speaks once, when he's being bludgeoned to death by Ferdinand.