<Li> Maria Doyle Kennedy as Siobhan Sadler, Sarah's and Felix's Irish foster mother; they call her "Mrs. S .". She fell in love with and married John Sadler at a young age, befriending his group of freedom fighters--the Birdwatchers . After John was murdered in a fight with her mother back in' 78, Siobhan started a new relationship with Carlton . She acts as guardian to Sarah's daughter Kira while Sarah is away . She is shown to be intelligent and resourceful, hiding Sarah for years and protecting her and Kira . Mrs. S used her network to hide Ethan Duncan and find Sarah as a child, claiming to have protected her from Dyad Sarah's whole life . Mrs. S makes a deal with Paul and the military to work with them and abduct Helena in exchange for a way to help Sarah and Kira . She eventually is forgiven by both sisters and is stunned as everyone else to learn that the genetic original for both clone lines is her mother Kendall Malone . Biologically speaking, Siobhan is Sarah's niece and that would make Kira her cousin . Siobhan later has her mother sent to Iceland, where Cal and Kira are hiding out . After Kendall is murdered by Marty Duko, a vengeful Siobhan eventually kills him . In the final stages of the clones' war with Neolution, Siobhan persuades Rachel to double - cross her lover Ferdinand, leading to a confrontation in which Siobhan and Ferdinand killed each other . </Li> <Li> Évelyne Brochu as Dr. Delphine Cormier, Cosima's monitor, girlfriend, and fellow scientist . She is torn between her job at Dyad and her love for Cosima . After finding out about Cosima's illness she works with her in the Dyad to try to find a cure . She is promoted to the public leader of Dyad after Leekie's death and unintentionally helps Rachel kidnap Kira . Rachel then bans her from working with clones and tries to send her away to Frankfurt . However, Marion promotes Delphine to take over Rachel's position and Delphine enacts her revenge on Rachel . Delphine returns to Dyad, supposedly after learning that Sarah was kidnapped and has been missing for five days, but it is later revealed that her jealousy has led her to spy on Cosima and Shay's relationship, photographing and videotaping the two on their various dates . Delphine interrogates Shay, believing her to be the Castor mole . She is about to begin cutting Shay when Cosima calls to inform her that Gracie admitted to being the Castor mole . Delphine finds out that Dr. Nealon replaced Rachel with an induced Krystal and sent her to Vienna . She confronts him in an enclosed room, and he reveals that Rachel now belongs to Neolution, the group that he has been working for all along, attempting to procure the Leda and Castor original genomes for scientific advancement . Delphine calls for the guards to take Nealon away, but she receives no responses, and Dr. Nealon suddenly attacks her as he bleeds from the mouth . He leans over her, spilling blood onto her face, as a regurgitated worm spills from his mouth . Delphine shoots Nealon before the worm can reach her . As he dies, he proclaims that Delphine will be dead before morning . Delphine confronts Shay to apologize and tells her that she is giving Cosima permission to reveal everything to Shay, stating that the two are right for each other . She then visits Cosima at Bubbles, discreetly saying goodbye to Cosima and the other Leda clones . Delphine parks her car in a parking garage and is followed by unseen pursuer . Delphine asks "what will happen to (Cosima)?" and receives no response; instead, the pursuer shoots Delphine, whose death is implied but not seen . Krystal confirms in season 4 that Delphine was picked up, alive, by after being shot . She has been on the Island in the north this whole time after being spared by PT Westmoreland, she reunites with a hypothermic Cosima . (recurring seasons 1 & 4--5; regular seasons 2--3) </Li> <Li> Ari Millen as a number of male clones (see here)--the result of a sister project to Project Leda: Project Castor, a top - secret military program . Unlike their Leda counterparts, the Castor clones have always been aware of what they are, being raised together by the US military; their caretaker was Virginia Coady, who they refer to as Mother . They suffer a mental defect, which basically turns their brains to, quoting Scotty, "Swiss cheese" after set amount of time; unfortunately the defect is also an STD, which sterilizes women . Coady studies this, often sending Rudy off on leave to infect new test subjects . The first Castor clone to be introduced to the viewers is Mark Rollins, coming off as a homicidal Prolethean, before being exposed as an undercover Castor agent; he marries fellow Prolethean Gracie Johanssen after running away from the Prolethean farm, wanting a normal life with her before his defect kills him . Other major Castor clones includes the menacing scarefaced Rudy, the tormented Seth, the crippled Miller and the Neolutionist Ira . All the Castor clones are now deceased, with Mark, the last, executed by Coady . (recurring season 2; regular season 3--5) </Li> <Li> Kristian Bruun as Donnie Hendrix (né Chubbs), husband to Alison Hendrix . He was once Alison's monitor, working for Dyad . His and Alison's marriage was strained for a long time, especially after Alison cornered him and tortured him to find out if he was a monitor or not . He lied, and they reconciled . However, she then found out the truth: that he really was a monitor but was unaware of his true purpose and that Alison was a clone . He then cornered his boss, Dr. Leekie, in his car and killed him with an accidental pistol shot to the head . He fled back to Alison, begging her to help him do away with the body . They buried Leekie under their garage . This "bonding" helped to jump - start their relationship, giving it newfound passion, trust, and happiness . In season 3, he got fired after telling his boss Susan Teller that she was a bitch, something he found "frickin' glorious". He and Alison later briefly sold drugs for Pouchie, and got the Hendrix family soap store Bubbles from Ali's mother . Helena comes to live with them, and Donnie comes to see that she means well; he even helps find her boyfriend as a "thank you" present . After Pouchie's niece threatens Oscar and Gemma, Donnie is left with all the drug lord's money after Helena murders them to protect the children . (recurring seasons 1--2; regular season 3--5) </Li>

Who plays the boy clones in orphan black