Nyssa of Traken, or simply Nyssa, is a fictional character played by Sarah Sutton in the long-running British science fiction television series Doctor Who. She was a native of the planet Traken, a world that was so peaceful that evil literally calcified in its atmosphere. Nyssa was the daughter of Tremas, one of the Traken Union's Consuls. A companion of the Fourth and Fifth Doctors, she was a regular in the programme from 1981 to 1983.

Nyssa was a child of privilege, gifted with a brilliant intellect, an expertise in bioelectronics, and a gentle, sensitive and compassionate soul. She was often the peacekeeper among the crew of the TARDIS, serving as a calm center to her fellow companions, Adric and Tegan. Nyssa was introduced in the Fourth Doctor serial The Keeper of Traken .

During the events of that story, her father's body was usurped by the life force of the renegade Time Lord known as the Master. Nyssa was subsequently transported to the planet Logopolis in the serial of the same name and witnessed her planet being consumed by a wave of entropy that was sweeping the universe. She was then present when the Fourth Doctor regenerated into his fifth incarnation, and continued to accompany the Fifth Doctor.

Adric's death in Earthshock was a severe blow to her, as it was to Tegan. However, she faced what her adventures with the Doctor had to offer 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 would leave the TARDIS during the events of Terminus, to help the leper colony station Terminus find a permanent cure for Lazar's Disease.

Nyssa's fate after she left the TARDIS is not known, although the spin-off novel Asylum, by Peter Darvill-Evans, revealed that she eventually left Terminus and settled down as an academic in a university on an unspecified planet.

Sarah Sutton returned as an image of Nyssa seen during the Fifth Doctor's regeneration scene in The Caves of Androzani, and next played the character in the 1993 charity special Dimensions in Time. Since then, Sutton has also voiced Nyssa in several audio plays alongside Peter Davison as the Fifth Doctor, produced by Big Finish Productions. The canonicity of the audio dramas, like other Doctor Who spin-off media, is unclear.

• Travelled from: The Keeper of Traken to Terminus