As mentioned above, the Mord-Sith were elite female torturers forced to serve Darken Rahl, but Richard Rahl freed them at the end of Wizard's First Rule. They now serve Richard by choice, out of gratitude.
Girls who are trained and become Mord-Sith are recruited by other Mord-Sith, usually based on tips from the girls' neighbors. The girl has to be someone with great compassion for others before her training, because these become the cruelest when broken (Cara says this in Temple of the Winds).
There are three stages of Mord-Sith training, each of which breaks the girl in a different way. First, the girl's spirit is broken by a trainer, then she watches her mother tortured to death to break her empathy, then she must torture her father to death to break her fear of hurting another (the training is outlines in Wizard's First Rule).
Mord-Sith wear skin-tight brown leather, except for special occasions. They always wear red armor when training so that the blood doesn't show, and white armor is a symbol that a pet has been broken. This is mentioned in Wizard's First Rule and every other book.
Note: Terry Goodkind seems to use Mord-Sith with and without the dash, but my informal research indicates the dashed form is most common so I'll use that.
The Mord-Sith mentioned by name in the series
are, in order of appearance:
- Denna: captures and breaks Richard in Wizard's First Rule, but he has partitioned his mind so he is able to recover. He kills her to get his magic back, which she asks him to do to end her torment. He wears her Agiel in her memory. In Stone of Tears, she appears to Kahlan in the Mud People's spirit house. She takes the Keeper's mark from Richard, in exchange for which Kahlan agrees to convince him to go with the Sisters of the Light. Before Richard left, he gives her Agiel to Kahlan.
- Constance: one of Denna's friends, and they occasionally torture him together. She tries to kill Richard as he is escaping the People's Palace in Wizard's First Rule, but he kills her with Denna's Agiel.
- Cara: first appears in Stone of Tears and helps Richard Rahl at the People's Palace. In Blood of the Fold she leads Berdine, Hally, Raina, and two soldiers to protect Lord Rahl in Aydindril and becomes a major character. From then on she stays with Kahlan and/or Richard.
- Berdine: In Blood of the Fold, she is captured by Tobias Brogan's magic, but Richard heals her. She and Raina are lovers. Throughout the rest of the series, she helps Richard translate Kolo's journal, although she appears less in later books.
- Hally: dies almost immediately in Blood of the Fold after a battle with mriswith.
- Raina: Berdine's lover. Dies in Temple of the Winds.
- Rikka: arrives in Aydindril at the end of Temple of the Winds. She helps Kahlan and Cara lead the fight against the Imperial Order in Faith of the Fallen.
- Hania: captured by the Imperial Order in Faith of the Fallen. Nicci promises to kill her in exchange for information about Richard's time with Denna.
- Nyda: tricked into helping Jennsen evade Nathan Rahl and escape the People's Palace in The Pillars of Creation.
The four Mord-Sith who come to Aydindril in Blood of the Fold are Cara, Hally, Raina, and Berdine.