Vislor Turlough

Vislor Turlough — more commonly known as just "Turlough" — was a companion of the Fifth Doctor. He principally travelled alongside Tegan Jovanka, but also had a few adventures with Nyssa and Kamelion. He briefly met and saved the life of Peri Brown before departing the Doctor's company. He also had significant interaction with Brigadier Lethbridge-Stewart, the First Doctor and Susan Foreman. He encountered, but did not speak with, the Second and Third Doctors and Sarah Jane Smith.

Turlough was a complex individual. His motivations were often unclear to those around him. He was for a time and by his own choice under the influence of the Black Guardian. During this period, he actively tried to kill the Doctor. After overcoming the Black Guardian, he was a mostly-trusted member of the TARDIS crew, but there remained instances where his actions were questioned. It was only at the end of his time on the TARDIS that the Doctor finally discovered the truth about how Turlough ended up on Earth, and why he was susceptible to the Black Guardian in the first place.

The Doctor once indicated that what made Turlough such an interesting travelling companion was that he never knew what Turlough was thinking.

Early Life
Little is known about Turlough's life on Trion before and during the civil war, although his desperation to destroy a distress beacon he recognised as being from Trion and his reluctance to contact his own people to save the people of Sarn, indicate there were severe penalties for him evading his exile. It can be assumed he was an active member of the military; he held the rank and serial number of "Junior Ensign Commander Vislor Turlough. VTEC9/12/44". (DW: Planet of Fire) His mother was killed during the civil war and his younger brother Malkon and his father were exiled to the abandoned colony planet of Sarn. Turlough himself was exiled to Earth. (DW: Mawdryn Undead)

Meeting the Doctor
On Earth he lived as a human schoolboy, hiding his alien origins and attending Brendon Public School, where Alistair Gordon Lethbridge-Stewart taught. Turlough was under the supervision of a custodian masquerading as a solicitor in Chancery Lane. He was contacted by the Black Guardian, who offered him his freedom in exchange for the death of the Fifth Doctor. Turlough subsequently ingratiated himself with the Doctor and his companions Nyssa and Tegan Jovanka, assisting in resolving a time paradox, after which he was invited to join the Doctor in his travels. (DW: Mawdryn Undead)

With the Doctor
In subsequent adventures, Turlough received several messages from the Black Guardian, reminding him of his obligation to kill the Doctor - an act he became loath to do as he grew fonder of the Time Lord. Finally, he destroyed a prize that would have guaranteed his freedom and his pact with the Black Guardian rather than kill the Doctor, ending his association with the villain and becoming a loyal member of the Doctor's team. (DW: Enlightenment)

It was after breaking away from the Black Guardian that Turlough's outlook changed from self-preservation to wanting to help others. This led him to actions such as deliberately putting his own life at risk to save the Doctor and Tegan (DW: Warriors of the Deep), facing the demons of his own people (DW: Frontios) and finally accepting personal responsibility and trading his own freedom to save the lives of the population of Sarn. (DW: Planet of Fire)

Although he initially expressed a desire to return to his homeworld and at one point asked the Doctor to take him home (DW: Enlightenment), after he had spent more time travelling with the Doctor he grew reluctant to return. He destroyed a distress beacon from a Trion ship, attempted to disable Kamelion, whom he believed was reacting to the beacon, and was reluctant to contact his own people. (DW: Planet of Fire)

After discovering that his younger brother was still alive, and that the persecution of political prisoners had long been abandoned on Trion, Turlough finally left the TARDIS to return home, after effectively putting the Doctor ("who gets into the most terrible trouble") in the hands of new companion Peri Brown. (DW: Planet of Fire) Later, as he regenerated, the Doctor had visions of several of his past companions, including Turlough. (DW: The Caves of Androzani)

Life after the Doctor
Not much is known of Turlough's life after he left the Doctor. It is known that soon after his return to Trion he became involved in an adventure to save his homeworld and Earth. (TC: Turlough and the Earthlink Dilemma)

At one point an enemy of the Doctor's tenth incarnation produced a diary purporting to be Turlough's, though the Doctor had no recollection of Turlough keeping one. (IDW: Tesseract, IDW: Don't Step on the Grass) The Doctor and Emily Winter travelled to Trion, where they met with Turlough to confirm the diary wasn't his. (IDW: Final Sacrifice)

A possibly apocryphal account suggested that Turlough might have briefly travelled with the Doctor in his sixth incarnation alongside Peri. (Crisis in Space)

Personality
Turlough was selfish, always shielding himself from blame. (DW: Mawdryn Undead) He could lie convincingly to most; some, such as Tegan and the Brigadier, were not taken in by him. (DW: Mawdryn Undead, Terminus)

Tegan did not like Turlough, finding him untrustworthy. She did not approve of the Doctor letting Turlough consider the Black Guardian's offer, believing that Turlough would choose the crystal. However, the Doctor was confident in Turlough's morals. (DW: Terminus, Enlightenment)

Despite this, he recognised the Doctor's good intentions; he tried to make the Black Guardian reconsider his order to kill the Time Lord. (DW: Terminus, Enlightenment) Turlough used the tranquil Eye of Orion to paint. (DW: The Five Doctors) He understood the TARDIS systems well enough to run a diagnostic in DW: The Five Doctors and programmed the TARDIS to rescue the Doctor and Peri in DW: Planet of Fire.

Turlough decided to stay with the Doctor. He told him he could learn more with him. (DW: Warriors of the Deep)

Behind the scenes

 * Turlough was the last male companion to travel with the Doctor on-screen until Adam Mitchell, who joined in Dalek in 2005.
 * Turlough was the last in seven-year run of non-human televised companions that inhabited the TARDIS, beginning in 1977 with K9 Mark I. Others included K9 Mark II, Romana I, Romana II, Adric, Nyssa and, nominally, Kamelion.
 * Turlough was also one of the few companions that could operate some TARDIS systems on his own. He could tell the instruments were functioning properly in The Five Doctors and set the TARDIS controls to retrieve the Doctor and Peri in Planet of Fire.
 * Turlough was the first red-haired companion in the Doctor's history. Mark Strickson himself was not ginger. He dyed his hair for the role.