Nyssa

Nyssa of Traken, or simply Nyssa, was a native of the planet Traken, the homeworld of the Traken Union and daughter of the respected Consul Tremas. When Tremas "died", taken over by the Master, and she had nowhere to go, she travelled with the fourth and then the fifth incarnations of the Doctor.

Profile
Nyssa was a child of privilege, gifted with a brilliant intellect, an expertise in bioelectronics, and a gentle, sensitive and compassionate soul. She first met the Doctor and Adric as they defeated the Master, who had already subverted the will of Nyssa's mother, Cassia. The Doctor and Adric defeated him, but subsequently, her father's body was usurped by the Master's life force and taken over, after which he left Traken. (DW: The Keeper of Traken)

While Nyssa still remained unaware of this, the Watcher would take her in the Doctor's TARDIS to the planet Logopolis where she witnessed her planet being destroyed by a wave of entropy. She was present when the Doctor regenerated into his fifth incarnation, and continued to accompany him afterwards along with Adric, who she had early met, and Tegan, a Human from Earth. (DW: Logopolis)

She and Tegan gave crucial assistance to the the newly-regenerated Doctor, effectively representing his scientific side while he went through his troubling regeneration. (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)

Adric's death, shortly after, (DW: Earthshock) was a severe blow to her, as it was to Tegan. Tegan herself vanished, due to an oversight of the Doctor's (DW: Time-Flight) after which she and the Doctor travelled together. Nyssa coped with her newly-awakend telepathy and also witnessed, with the Doctor the birth of her universe's Cybermen on their world of origin, Mondas (BFA: Spare Parts)

By chance, they re-joined Tegan in Amsterdam (DW: Arc of Infinity) Nyssa faced the challenges of her adventures with the Doctor with both determination and the serenity of her Trakenite birthright, turning her sadness in being the last of her people into a desire to help others. It was appropriate, therefore, that she left the TARDIS to help the crew of Terminus to find a permanent cure for Lazar's Disease. (DW: Terminus)

She would she eventually leave Terminus and settled down as an academic in a university on an unspecified planet. (PDA: Asylum) Eventually, she married and had children. During this later period of her life, she reunited with the Doctor and again assisted with his regeneration. (BFA: Circular Time)

Her secret life on Earth
The excessive time rift activity in Cardiff, a year-and-a-half ago, led Nyssa and her children to cross over from the planet she was residing on to contemporary Earth. Realising that they couldn't return home again, she assumed a human name and took a job somewhere in Britain as a teacher.

Personality
More mature than her fellow travelers, apart from the Doctor, She did not brag about her scientific knowledge or believe that it made her superior to others. Tegan noted that Nyssa preferred to "care and share", which Tegan sometimes found intrusive and not her style. (MA: Goth Opera) Nyssa was often the peacekeeper among the crew of the TARDIS, though she often found Adric irritating at times. She had probably the closest relationship with this incarnation of the Doctor of any of his companions. Nyssa's nature made it a bit hard at times for her to relax and enjoy herself. 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)

Key Life Events

 * Nyssa meets Adric and the Doctor on Traken. (DW: The Keeper of Traken)
 * Nyssa joins the crew of the Doctor's TARDIS. Entropy destroys Traken. The Doctor regenerates into a new form (DW: Logpolis)
 * Adric dies. (DW: Earthshock)
 * Nyssa decides to stay behind on Terminus. (DW: Terminus)