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.

Life on Traken
The daughter of Councillor Tremas and Cassia, Nyssa was a child of privilege on Traken, the center of the Traken Union. She was gifted with a brilliant intellect, an expertise in bioelectronics, and a gentle, sensitive and compassionate soul. Nyssa 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. Subsequently, the Master left Traken. (DW: The Keeper of Traken)

Travels
Not long after, the Watcher removed Nyssa via the Doctor's TARDIS to the planet Logopolis. There, she witnessed her planet being destroyed by a wave of entropy. She was also present, with Adric and Tegan Jovanka, a Human from Earth, when the Doctor regenerated into his fifth incarnation. (DW: Logopolis)

With Tegan, she gave crucial assistance to the the newly-regenerated Doctor, effectively representing his scientific side while he went through his troubled regeneration. (DW: Castrovalva) Having no home any more, Nyssa joined the crew of the TARDIS. 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)

The death of Adric, a futile self-sacrifice against the Cybermen (DW: Earthshock), was a severe blow to Nyysa, as it was to Tegan. Tegan herself vanished, left behind due to an oversight of the Doctor's (DW: Time-Flight). After this, the Doctor travelled together. Nyssa coped with her newly-awakend telepathic powers (BFA: Winter for the Adept, Primeval) and also witnessed, with the Doctor the birth of the Cybermen on their world of origin, Mondas (BFA: Spare Parts)

By chance, the Doctor and Nyssa met Tegan again 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)

After her travels
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)

Personality
Apart from the Doctor, Nyssa had more maturity than her fellow travelers. 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 way. (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: Logopolis)
 * Adric dies. (DW: Earthshock)
 * Nyssa decides to stay behind on Terminus. (DW: Terminus)
 * Nyssa marries and has children. (Mentioned BFA: Circular Time)