Gareth Jenkins (in-universe)

In the 1980s, Gareth Jenkins was an eight-year-old boy from Milton Keynes, Buckinghamshire, who wrote into the BBC One audience wish-fulfilment programme, Jim'll Fix It. His request was to meet Colin Baker and see the TARDIS interior set in-person. He enclosed a portrait with the letter, showing that that he already had a complete Sixth Doctor's costume which his grandmother had made for him.

The producers of Jim took Jenkins' request further, and worked with John Nathan-Turner's staff at Doctor Who to create a sketch around the boy, A Fix with Sontarans. Jenkins; in his kid-sized Sixth Doctor's costume; did indeed play a major role in it, opposite Colin Baker and Janet Fielding. By the time the sketch was filmed however, Jenkins' growth spurt in the interim was demonstrated by the prominent gap between his sweater-vest and trouser waist, and by his trouser cuffs exposing most of his yellow spats.

The mini-episode began – unlike most mini-episodes of the later BBC Wales era – with the series' full opening credit sequence. Janet Fielding's name was omitted from the intro entirely, as was the norm for actors on Doctor Who until 1996. In this instance, however, the intro displayed "starring Colin Baker", followed by "with Gareth Jenkins". Jenkins and Baker thus hold the distinction of being the only two actors billed in the Doctor Who title sequence in the first thirty-three years of the series' history (apart from Derrick Sherwin who acted in a cameo role during the period in which he was credited in his regular capacity as the series' producer).

A Fix with Sontarans concluded with the opening of the TARDIS' doors and the end of Eric Saward's script. The 69 seconds which continued thereafter comprised something entirely separate and intrinsically outside of the DWU, being an instalment of Jim'll Fix It on the Doctor Who set, with host Jimmy Savile welcoming actors Gareth Jenkins, Colin Baker and Janet Fielding to his programme. Baker presented Jenkins with both a Jim'll Fix It medal and, as an added treat, the "BBC meson gun" prop to keep.

Jenkins' appearance is included among the archival footage shown in the 2006 documentary short, Built for War, an extra feature of The Sontaran Experiment DVD.

He is not related to the Gareth Jenkins who works with Big Finish Productions.

Gareth Jenkins, the "character"
While A Fix with Sontarans is regarded as non-canon, writer Eric Saward's story itself could – at least conceivably – be viewed as occurring within the televised Doctor Who continuity. The fictional Gareth Jenkins character who is seen on-screen until Savile's arrival, can be considered as entirely separate from the actor Gareth Jenkins who portrayed him and who was interviewed out-of-character by Savile.

Jenkins explains that his skill with the TARDIS console comes from having watched the Doctor operate the TARDIS on telly, but he makes no mention of the series, the actors, the BBC, inter alia. (TV: A Fix with Sontarans) Consequently, he might well have been referring to a time-space visualiser which was called a "time television" by Barbara Wright who coincidently watched Jimmy Savile on such a device. (TV: The Chase part 1 "The Executioners") Thus, Jenkins could have conceivably watched anything the Doctor did during the Earth's relative past. (i.e. from the Big Bang circa 13.75 billion BCE (TV: Castrovalva) through the Fifth Doctor's 1984 parting with Tegan at Butler's Wharf. (TV: Resurrection of the Daleks'')

Biography:

 * As a boy, Gareth Jenkins learns how to operate the TARDIS' controls by watching the Doctor do so on telly (possibly a "time television").
 * He mimicks the Sixth Doctor's preferred, garish attire.
 * The Sixth Doctor and Tegan Jovanka accidentally teleport him from Earth (presumably circa 23 February 1985) to the Doctor's TARDIS. He reveals himself to a far more familiar with TARDIS console than Tegan is.
 * While aboard the TARDIS, the young Jenkins is seen by Group Marshall Nathan as a vital enemy to be obliterated before he can kill the Sontarans in the future – much like River Song in her "Mels" incarnation and the Teselecta each attempted to kill Adolf Hitler in 1938 before he could trigger the European portion of the Second World War in 1939; and River/Mels herself was targeted both as the newly regenerated River Song by the Teselecta minutes later, and as young "Melody Pond" by her own (unknowing) mother in 1969, before she was to kill the Eleventh Doctor in 2011. (TV: Let's Kill Hitler, The Impossible Astronaut)
 * He kills the two Sontarans in self defence, his viewings having revealed which switches to press for that purpose.
 * Moments later, he, Tegan and the Doctor see an horrific visage suddenly appear on the TARDIS monitor: Like Ian Chesterton, Barbara Wright and Vicki Pallister during the Doctor's first incarnation before them, (TV: The Chase part 1 "The Executioners") he and Tegan look upon the face of Jimmy Savile, now twenty more years the worse for wear. Tegan and the Doctor respectively describe the sight as "monstrous" and "revolting", before the Doctor inexplicitly activates the TARDIS' inner doors and allows the horrendous creature entry into the control room.
 * When the Sontarans invade Earth in 2001, the adult Gareth Jenkins leads a resistance movement which turns away the invasion fleet. (TV: A Fix with Sontarans)