Stahma Tarr is Datak Tarr’s wife and a member of the Castithan alien species. On the surface, she is beautiful, loyal, and the perfect picture of a Castithan wife. Beneath the surface, however, lies a different side that is ready to break free from the traditional subservient role assigned her by her caste.
Stahma Tarr comes from old money and is very cunning. Her role was described as being very Lady Macbeth. Stahma is not satisfied with Datak’s station in Defiance and feels he (and by extension, she) should have more power. Joshua Nolan quickly realizes that she is far more dangerous than her husband after only a few weeks in town.
The Votanis System and Journey to Earth
Stahma was born a member of the ruling Shanje Liro to a relatively prominent family. In her youth, Stahma mentioned that she was quite good at a sort of Castithan poetic performance, even having a small loyal following. Unfortunately, her talent was good enough to eventually attract her father's attention, who immediately put a stop to it since performance was not proper for a woman of her rank.
On Casti she attended an academy where the fudano taught them that Rayetso demands that no misdeed go unpunished.
During her voyage to Earth on an Ark, Stahma was engaged by her parents to a man "of honor", though Stahma herself was not particularly attracted to him. During the voyage, she met her future husband, Datak, who she described as a 'scruffy nobody who had won passage in payment for a gambling debt". Datak pursued her shamelessly, until Stahma's fiance challenged him to a blood duel. However on the way to the duel, her fiance was mysteriously flushed out of an airlock. Stahma tells this story to Christie Tarr who expresses doubts as to the tale's veracity, suggesting his death wasn’t actually a mystery. Later, Stahma says to Alak, "Once again the Castithan males falter and I am left to open the airlock door myself," suggesting that she did in fact murder her fiance.
The Pale Wars
During the Pale Wars, Stahma aided Datak in his business on Earth eventually giving birth to her only child Alak. When the war ended, the two found themselves among a group of migrants who eventually settled in Defiance.
Over the years, Stahma helps Datak to build a business and reputation in Defiance, but she is still not satisfied with Datak's station in life and feels that he (and by extension, she) should have more power. Stahma perfectly plays the part of the dutiful wife while secretly harboring her own ambitions. Unlike her husband, she gains a much greater understanding of human cultures and social norms, likely realizing that she would eventually need to balance his wholesale rejection of anything human with a more pragmatic view.
Stahma Tarr is first seen in the Pilot episode, proudly seated beside her husband as Mayor Amanda Rosewater publicly thanks him and Rafe McCawley for sponsoring a statue in honor of the Defiant Few, a group of human and Votan soldiers who helped to end the Pale Wars. After the celebration, Datak is upset that his primary rival, Rafe McCawley, packed the crowd to get a greater applause than Datak. Stahma flirts with him and works to calm his temper by suggesting Datak's just upset he didn't think of it first. The discussion quickly turns to their son, Alak. While Datak is concerned that Alak is running with a bad crowd and will ruin both their reputation as a family and the life Datak has built for him, Stahma thinks it is natural for young people to push boundaries and isn't worried.
Alak & Christie
Stahma soon learns that Alak is dating Rafe McCawley's daughter, Christie. Datak is outraged by the idea of his son dating his rival's daughter, but Stahma convinces him that the relationship would serve as a key strategic move. Stahma reminds Datak that mining is a dangerous job, and if anything were to happen to Rafe, his children would inherit the mines. And if Alak and Christie were married, her wealth would be Tarr wealth. The only problem, Rafe McCawley must die first. The implication is clear. Later, as Datak and Stahma watch Alak place an engagement ring on Christie's finger, Datak says, "This will kill Rafe McCawley" to which Stahma replies, "Eventually, yes. If we're clever and patient."
While Datak shows no interest in Christie, Stahma is more forgiving of Christie's human customs and attempts to forge a relationship with her son's fiancé. In order to ensure the marriage takes place, Stahma encourages Christie to defy her father. Rafe does not want Christie to marry Alak, so Stahma tells a dark story of how she chose Datak as her husband despite her own family's disapproval. Although Stahma is still motivated by a desire to claim Rafe's mines, Stahma welcomes Christie into her life with open arms by including her in family diners and not judging Christie for her minimal understanding of Castithan culture.
Later in the season, Rafe McCawley declares that he will leave the mines to the Irathients when he dies, thwarting Datak and Stahma's plans. Although Datak is initially upset, Stahma encourages the wedding to go forward, and the two are married in a ceremony that mixes human and Castithan tradition. As Christie prepares to walk down the isle, Stahma calls Christie her hanya tavo (heart daughter).
Tarrs & Rosewaters
In episode 4, Kenya Rosewater is kidnapped, forcing Amanda and Nolan to seek Datak's help in finding her. While Datak bristles at the idea of helping people who do not respect him, Stahma talks to Amanda in private. With a soft smile, she tells Amanda that she would be willing to help recover Kenya in exchange for a town council seat for her husband. Stahma says, "Your sister is a very special young woman. I'm rooting for her," before walking away, leaving Amanda speechless. Although Stahma thinks highly of Kenya, her first priority is securing power for her husband. Amanda reluctantly agrees, but this is how she and Nolan realize how powerful Stahma is. At the end of the episode, Nolan tells Stahma, "I've had my eye on the wrong snake. You're the dangerous one" to which Stahma replies, "you're very sweet."
Only a few episodes after this incident, Stahma goes to the NeedWant where Kenya works as a prostitute. Stahma wants to purchase time with Kenya for Alak in preparation for his wedding night. Kenya laughs, but Stahma is unaware of how strange this request sounds to a human and is therefore extremely offended by Kenya's response. Kenya apologizes and asks Stahma to have a drink with her.
While Stahma and Kenya enjoy a bottle of wine, Kenya encourages Stahma to prioritize her own desires rather than thinking solely of her husband and her son. Stahma reveals that she used to recite poetry, something Kenya would love to see her take up again. Kenya then asks Stahma to dance, and although the audience does not see the dance, Kenya and Stahma are next seen in bed together, sharing a soft kiss. Kenya playfully says, "Can you imagine if Datak could see us right now?" Stahma then turns deadly serious, warning Kenya that Datak would kill them both if he ever caught them together. Stahma once again echoes this sentiment the next time she sleeps with Kenya, but she worries that Kenya does not understand just how much danger she would be in if their secret got out.
During their relationship, Kenya comes to see Stahma as a victim of abuse by a husband with double standards (Datak is allowed to sleep with prostitutes, but Stahma is not). Kenya hates that Datak hurts Stahma, but Stahma insists that Kenya simply does not understand Castithan marriages. She says that she loves Datak for his cruelty because it proves he’s willing to do anything to achieve his goals.
In episode 9, Amanda Rosewater falls ill with a dangerous virus, and once again, Stahma takes the opportunity to manipulate Amanda to better her husband's career. Datak underhandedly takes charge so that he looks like a hero. He then uses the situation to jump start his mayoral candidacy, becoming Amanda's opponent. As he gives his speech to the town, Stahma mouths along to his words, implying she is behind the speech.
With Election Day rapidly approaching, Stahma once again proves that although she cares deeply for Kenya, her first priority is her husband. As part of a scheme to destroy Amanda's career, Stahma tells Kenya that Datak is planning to have Amanda killed. Kenya behaves exactly as expected by reporting the threat to Nolan and Amanda. Stahma and Datak also tell Alak to get one of his friends to shoot Amanda with a paintball gun during an upcoming speech. Although the teenagers think it's all a joke, Datak and Stahma know that Nolan will respond as if its a serious threat, and that's exactly what happens. Nolan shoots Alak's friend as soon as he aims the paintball gun at Amanda. Datak uses this as part of his quest to destroy Nolan's reputation, and by association, Amanda's.
Upon realizing Stahma used her to destroy both her sister and her friend, Kenya goes to Stahma in an outrage, threatening to tell Datak about their relationship. Although Stahma manages to dismiss Kenya for the moment, in the next episode Kenya tells Datak, "she's lovely. I'd keep an eye on her if I were you." Datak then realizes exactly where Stahma learned her new sexual skills. He's outraged, but still forces Stahma to put on a smile and vote for him. For the first time, Stahma seems genuinely terrified.
Later, Stahma takes Kenya into the woods, claiming she wants them to run away from Defiance together. Stahma hands Kenya a flask, but Kenya suspects it is filled with poison. Although she is correct, Kenya does not realize that Stahma put poison on the outside of the flask, and she dooms herself just by touching it. As Stahma waits for the poison to kick in, she admits that her relationship with Kenya was more than just sex for her. It was the first time she had opened herself up to a relationship outside outside her liro, and "it was exhilarating."
Although Datak wins the election, when Stahma returns from killing Kenya, she finds that Datak has committed a murder of his own. He has killed a high ranking member of the Earth Republic, and will be arrested as soon as he is discovered. He will never take office.
Datak tells Stahma that she is a good wife for murdering Kenya as he requested, but in the end, Stahma lost both her lover and everything she worked so hard to achieve in her husband's name. Her outlook on life is forever changed.
"Your father surrendered his claim on his financial interests when he murdered Colonel Marsh in a fit of foolish temper. I thought perhaps his son could take over with the proper guidance, but you lack the strength and brutality to do what is necessary... Once again, the strong Castithan males falter and I am left to open the airlock door myself! The family business belongs to me."
With her husband in prison for murder, Stahma steps up to run the family business, but because Castithan society is extremely patriarchal, Stahma must act in her son's name. She pushes Alak to behave as ruthlessly as she would, but grows frustrated by his kind nature. Alak tries to forgive employees and maintain their loyalty through friendship, but Stahma sees this forgiveness as a sign of weakness. Ultimately, Stahma decides that she is better equipped to run the family business than both her husband and her son. She commands Alak to do exactly as she says until the day Castithan men learn to follow the leadership of a woman.
Caught in Rahm Tak's clutches, Stahma and Datak conspire against the town, blow up the arch, and earn the further wrath of Amanda Rosewater, who already despises them for murdering her sister. Stahma quickly begins a relationship with T'evgin, the new Omec man in town, having fantasized of being swept away by an Omec man since she was young. She attempts to poison him, but that doesn't end their sexual relationship. She also murders her daughter in law, Christie, alienates her son, and mentors her young handmaiden, Andina.
- Stahma chose to speak with a mild mid-Atlantic accent, similar to that of a stage actor, after researching and choosing a specific accent that would not offend anyone different from her as she assimilated into the new world 
Once again, the strong Castithan males falter and I am left to open the airlock door myself. The Opposite of Hallelujah
Where you see kindness, others see weakness. The Opposite of Hallelujah
I come from a culture that worships dicks. This Woman's Work
I'd snap her like a twig. Bottom of the World
Your price is too high. I'll gut the little whore myself. Bottom of the World
Stahma: If your wife has harmed them, she will die an excruciating death.
Datak: And if she hasn't harmed them?
Stahma: Same outcome. I see your point. The World We Seize
This is a kwonyo gyendo [new world]. It will never conform to your traditions. The old ways are dead. When Twilight Dims the Sky Above