Tegan Jovanka was an Australian air hostess who became a travelling companion of the Doctor towards the end of his fourth incarnation and into his fifth incarnation.
Played by Janet Fielding, Tegan Jovanka debuted in the Doctor Who story Logopolis, the final story of Series 18, or Story 115 overall, which began airing on 28th February 1981. Logopolis marked the final tale of the fourth Doctor, played by Tom Baker, and Tegan became one of his companions just in time to see him regenerate into the fifth Doctor, played by Peter Davison. She would remain on the show until Series 21's Resurrection of the Daleks, departing at the end of the fourth and final episode on 15th February 1984.
Born and raised in Australia, Tegan Jovanka moved to London in 1981 when she was 20 to begin a career as an air stewardess. On her first day of work her aunt Vanessa was driving her to Heathrow Airport when their car broke down on the motorway. Pulling into a layby, they spotted what they thought was a police telephone box, and Tegan entered it, intending to use the phone within to call for help. However, the phone box was really the time-travelling Doctor's time machine, the TARDIS, and Tegan, finding to her surprise that the interior was far larger than it should be, managed to get temporarily lost inside. While she was there the Doctor's enemy, the rogue Time Lord the Master, who had lured the TARDIS to the layby as part of a trap, murdered Aunt Vanessa on a whim, and the Doctor, unaware he had picked up a new passenger, dematerialised the ship and set out into space. Involved by dint of her aunt's murder, Tegan worked with the Doctor and fellow travelling companions Nyssa and Adric to stop the Master from holding the universe to ransom, and witnessed the Doctor's regeneration after he fell from the Pharos Project's gigantic radio telescope.
Once the Doctor had recovered from his regeneration, Tegan demanded he return her home, but the Doctor's initial attempts to make it back to 1981 Earth were singularly unsuccessful, and Tegan variously visited a future Earth colony circa the 28th century, where they ran into the Doctor's seventh incarnation and his friends Chris Cwej and Roz Forrester, then the Urbankans' colony vessel, followed by the planet Deva Loka, where she was possessed by the malevolent psychic entity known as the Mara, then 1666 London, where she witnessed the Doctor accidentally start the Great Fire of London while trying to stop some stranded alien convicts from causing far greater devastation, and finally Cranleigh Hall in 1925 England. During this time Tegan became good friends with her fellow travellers, bonding especially closely with Nyssa. The Doctor however, while a friend, annoyed her with his inability to return her home, and she often grew frustrated with the frequently immature Adric, something she came to regret when Adric subsequently died when the TARDIS crew clashed with the Cybermen in the 26th century. Soon after this the Doctor finally made it back to 1981 Earth, and even to Heathrow Airport, where an investigation into mysteriously vanishing aircraft led to another confrontation with the Master. In the aftermath of this escapade, the Doctor and Nyssa swiftly departed, unaware that Tegan had changed her mind about leaving the TARDIS at the last second and had tried to rejoin them.
Tegan tried to return to her old life, but during a break from this to visit Amsterdam and meet her backpacking cousin, Tegan ran into the Doctor and Nyssa again, and, after helping them stop another rogue Time Lord, Omega, she resumed travelling with them. Almost immediately they discovered that vestiges of the Mara had remained hidden inside Tegan's mind, leading to another battle against the entity as it again seized control of her and tried to manifest itself in the physical world. Soon after this, the travellers twice ran foul of vampires, with both Tegan and Nyssa nearly falling prey to the supernatural afflication. After this adventure the Doctor encountered an old friend, retired UNIT commanding officer Brigadier Alistair Gordon Lethbridge-Stewart, and the TARDIS gained another traveller, the manipulative Turlough, an alien exiled to Earth who saw the Doctor as his way off a benighted planet, but who was also secretly being coerced into working against the Doctor by the cosmic entity known as the Black Guardian. Tegan instinctively, and rightly, distrusted the secretive Turlough. Shortly after this Nyssa left the ship, depriving Tegan of her best friend, but Turlough proved himself by standing up to the Black Guardian and thwarting his attempt to destroy the Doctor. Following this the travellers visted England in 1215, where they stopped the Master from interfering with the signing of the Magna Carta and picked up another traveller, the robotic shapeshifter Kamelion.
After a short vacation stop, the travellers were drawn to Gallifrey, the Doctor's home planet, when the Doctor's former mentor, the now-corrupt Borusa, abducted the Doctor's past incarnations and many of his former travelling companions. During this adventure Tegan met the Brigadier again, and briefly encountered the Doctor's granddaughter, Susan, and friend Sarah Jane Smith.
During the TARDIS' next few journies Tegan encountered the Sea Devils and Silurians in the late 21st century; convinced the Doctor to take her to visit her grandfather in rural England, where they ran into the mind-controlling alien Malus; encountered some bovine aliens on the Moon; met the Judoon when they landed near the Doctor's terrestrial house on Allen Road; and visited the planet Frontios, where some of mankind's last survivors were struggling to survive. However, when a trip back to 1980s Earth pitted them against the Daleks, Tegan was sickened by all the resulting loss of life, and tearfully quit the TARDIS.