Nyssa

Nyssa (formally, Nyssa of Traken) was a native of the planet Traken, the homeworld of the Traken Union. She was acquainted with the Fourth Doctor, but was mainly a companion of the Fifth Doctor. She also adventured with Adric, Tegan and, briefly, Turlough and the Brigadier.

The daughter of Consul Tremas, Nyssa was a child of privilege on Traken. She was gifted with a brilliant intellect, and specialized in bio-electronics.

Initial encounter with the Doctor
Nyssa first met the Doctor in his fourth incarnation when he was traveling with Adric. At the time, she was preparing to the celebrate the marriage of her long-widowed father to Kassia. Unbeknownst to her, the Master had also come to Traken, and was planning to exploit the tremendous power of the Keepership, to which her father was the only rightful heir. One of his main goals in doing so was to find a way to live beyond his last natural regeneration. While the Doctor and Adric did indeed prevent the Master from taking over the Keepership, they could not stop him from killing Nyssa's new step-mother. They also did not stop the Master from "killing" Tremas by transferring his essence into Tremas' body. The Master lived on, and Nyssa was orphaned in her young adulthood. (DW: The Keeper of Traken)

Travels
Not long after, the Watcher transported Nyssa to the planet Logopolis in the Doctor's TARDIS. There, she discovered that the Master had, in effect, killed her father. He then moved to enslave her mind, involving her in his complicated plan to take over the universe. Although the Doctor soon broke her free of the Master's spell, he then immediately entered into an uneasy alliance with the Master. Together, the two Time Lords and Tegan rushed back to Earth in the Master's TARDIS in an effort to halt the waves of rampant entropy that the Master had unleashed upon the universe. Adric and Nyssa were left with the Doctor's TARDIS on Logopolis. The Watcher helped Adric transport the duo back to Earth. En route, Nyssa learned that the entire Traken Union had been swept away by the growing entropy field which threatened the existence of every part of N-Space. She knew she was the last of her entire species by the time the TARDIS materialized on Earth. When she again met the Doctor, he had been mortally wounded in his successful battle to stop the Master. He regenerated, without ever having travelled with her in the TARDIS. (DW: Logopolis) Thus, she began traveling with the Doctor only after he had regenerated for the fourth time. Although she had comparatively little direct experience of the Doctor, she became integral to nursing him back to full health during the particularly troubled regenerative process. (DW: Castrovalva) Following an adventure with the Monarch, she fainted (DW: Four to Doomsday) on account of stress and spent a few days in recovery. (DW: Kinda) Thereafter, she discovered she had a look-alike in early 20th century England. (DW: Black Orchid)

The death of Adric (DW: Earthshock) was a severe blow to Nyssa, as it was to Tegan. While working through their grief, the TARDIS crew became embroiled in an adventure which sent a Concorde back through time. After they successfully returned the airplane back to 1980s Heathrow, the Doctor accidentally left Tegan behind. (DW: Time-Flight)

Nyssa and the Doctor then began traveling alone together. During this time, they had many adventures. On several occasions, Nyssa began to develop her nascent telepathic powers (BFA: Winter for the Adept, Primeval). She also witnessed the birth of the Cybermen on Mondas. (BFA: Spare Parts) For a time, the Doctor and she were joined by Thomas Brewster, a human male from Victorian London. (BFA: The Haunting of Thomas Brewster) This threesome had a few adventures — perhaps most notably one in which Nyssa discovered Adric did not die in Earth's prehistoric past (BFA: The Boy that Time Forgot) — before he voluntarily left the TARDIS to pursue a romance in 2008. (BFA: A Perfect World) Nyssa carried on traveling alone with the Doctor until she and the Doctor chanced upon Tegan in Amsterdam. During the same adventure, she forcefully stood up the Gallifreyan High Council on the Doctor's behalf. (DW: Arc of Infinity) Reunited, both she and Tegan traveled to Manussa in order to help Tegan rid herself of the returned influence of the Mara. (DW: Snakedance) She then helped the Doctor through a different sort of "regeneration crisis", during which she met the Brigadier and began traveling with Turlough. (DW: Mawdryn Undead)

She left the TARDIS under circumstances that were as tragic and noble as the ones that had accidentally forced her into the Doctor's company. After the TARDIS landed on the decks of the Terminus space station, the Doctor and she discovered that it was, in effect, a leper colony. She was the only TARDIS crew member who contracted the disease the station existed to treat. Just as she had always done with the tragedies in her life, she used her misfortune as a path to a better future. She opted to remain behind on the space station in order to help her fellow victims find a permanent cure for Lazar's Disease. (DW: Terminus)

After her travels
Although she believed she would die — though in her words, "not easily" —  on Terminus (DW: Terminus), Nyssa would eventually leave and settle down as an academic in a university on an unspecified planet. During this period, she encountered the Doctor's fourth incarnation again — bit long before he first met her on Traken (PDA: Asylum). Eventually, she married and had children with a man named Lasarti, who studied dreams. During this later period of her life, she reunited with the Doctor's fifth incarnation and again assisted with his regeneration into his next incarnation. (BFA: Winter)

Personality
Nyssa often seemed at once more mature and more naive than her fellow travelers. She did not brag about her scientific knowledge or believe that it made her superior to others. Nyssa faced the challenges of her adventures with the Doctor with both determination and the serenity of her Trakenite birthright. She turned her sorrow in being the last of her people into a desire to help others. Rarely did she mention any grief she might've been suffering as a result of her great misfortunes. Perhaps most extraordinarily, she never sought to revenge herself on the Master despite her many good reasons to do so.

Tegan noted that Nyssa preferred to "care and share". (MA: Goth Opera) Her trusting nature sometimes made her less alert to deception than Tegan (DW: Mawdryn Undead), but it also made her more adept at negotiating an effective balance between strong personalities. (DW: Earthshock, BFA: The Game) She had probably the closest relationship with the Fifth Doctor of any of his companions. Nyssa's near-royal upbringing and natural curiosity sometimes made it hard for her to relax and enjoy herself. Though her outlook usually tended to be rather serious, she did display a dry wit on numerous occasions, particularly when dealing with the Fifth Doctor's boyish idiosyncrasies.

She tended towards pacifism, though on one occasion she destroyed a Terileptil android (DW: The Visitation) and attempted to use the threat of violence in order to save the Doctor's life. (DW: Arc of Infinity) Even though her world and her people were destroyed, she always tried to live by the principles it stood for when she traveled with the Doctor.

Nyssa was considered to be one of the most intelligent companions and was one of the few companions capable of assisting with TARDIS operations.

Key Life Events

 * Nyssa meets Adric and the Doctor on Traken. (DW: The Keeper of Traken)
 * After having been left behind by the Doctor and Adric on Traken, the Watcher transports her to a reunion with the TARDIS crew on Logopolis. There, she meets Tegan Jovanka. Entropy, unleashed by the Master, destroys Traken. She is by the Doctor's side as he regenerates into a new form (DW: Logopolis)
 * She witnesses Adric's death. (DW: Earthshock)
 * Nyssa becomes the Doctor's sole companion. (DW: Time-Flight)
 * Nyssa meets Andrew Harper in Stockbridge, England, and has her first romantic relationship. (BFA: "Autumn")
 * After an apparently long period of absence, Tegan resumes her travels with the Doctor and Nyssa. (DW: Arc of Infinity)
 * Nyssa meets the Brigadier; Vislor Turlough joins the TARDIS crew. (DW: Mawdryn Undead)
 * Nyssa decides to stay behind on Terminus. (DW: Terminus)
 * Long after the events of Terminus, Nyssa meets a younger version of the Fourth Doctor than she had previously encountered in The Keeper of Traken. (PDA: Asylum)
 * At a point that may or may not be after the events of Asylum, Nyssa marries Lasarti and has children by him. (Mentioned BFA: Circular Time)

Behind the scenes

 * Nyssa was originally meant to have appeared only in The Keeper of Traken as a supporting character. She was therefore the sole creation of writer Johnny Byrne, to whom royalties had to be paid when the character was used. Like the Brigadier and K-9, she is a rare example of a series regular to whom the BBC does not enjoy sole copyright.
 * In the cover image for the upcoming Big Finish audio drama "Cobwebs", the photo for Nyssa is a recent picture of Sarah Sutton, suggesting that this story may be set following Nyssa's departure from the Tardis in Terminus. Possibly, she will be rejoining the still-young Tegan and Turlough as one of the Doctor's companions at a time long after their last meeting.
 * Peter Davison was known to have preferred Nyssa over any of his other companions. He intervened on several occasions when John Nathan-Turner attempted to write the character out of the series.
 * Perhaps in deference to Davison's affection for Nyssa, Big Finish greatly expanded Nyssa's role. They have built a network of stories in the televised gap between Tegan's departure in Time-Flight and her return in episode 2 of Arc of Infinity which was very much greater than it appeared on television. Starting with The Land of the Dead, the Fifth Doctor began a long series of audio adventures with Nyssa as his sole companion.
 * Like Tegan, Adric and the Fifth Doctor, Nyssa had been given a "costume" rather than a basic "look" by producer John Nathan-Turner. Nyssa's original costume narratively originated on Traken, and suggested her high-born status. It consisted of a maroon velvet jacket, a diaphanous, iridescent skirt, and multi-pastel, high-heeled shoes. It was further accessorized with an ornamental hair comb and a wooly purse. In terms of the order in which the episodes were broadcast, this look persisted through the end of episode 2 of Castrovalva. However, long before this episode had been filmed, it had been determined that the actor would need more practical clothing for the physical demands of her now-co-starring role. Therefore, she exchanged her skirt for a pair of maroon trousers, lost the purse, and began wearing lower-heeled shoes. According to production notes on the DVD release of the preceding story, Logopolis, the second iteration of Nyssa's "royal Traken" look was inspired by a rehearsal in which actress Sarah Sutton wore Nyssa's top, but her own corduroy pants. Thereafter, she also lost her hair comb. She completely abandoned the "royal Traken" look in Snakedance, and subsequently changed her look every story until her departure in Terminus. Famously, the costume for this final outing was mostly just the slip she had been wearing under her Mawdryn Undead dress.