Gareth Jenkins (in-universe)

Gareth Jenkins was a young child from 20th century Earth who enjoyed watching the Doctor's adventures on television, and found himself helping the Sixth Doctor defeat a duo of Sontarans when he was accidentally teleported aboard the Doctor's TARDIS.

He may have also been the leader of the Earth Defence Force by the 21st century, thwarting the Sontarans' invasion of Earth in 2001.

Biography
Gareth watched a series about the Doctor on television that taught him the various controls on the TARDIS control console. He also obtained a replica of the Sixth Doctor's coat. (HOMEVID: A Fix with Sontarans)

Meeting the Doctor
On 23 February 1985, (PROSE: Fixing a Hole) Gareth found himself brought aboard the Doctor's TARDIS in the midst of the Sontaran Group Marshal Nathan and his subordinate attempting to destroy it with a vitrox bomb, having accidentally been teleported onboard by Tegan Jovanka pressing the wrong button on the control console. While the Doctor was reluctant to have Gareth help, he let Gareth help him set a lethal trap for the Sontarans.

After the Sontarans arrived, they recognised Gareth's name as belonging to the leader of the Earth Defence Force who thwarted their invasion in the year 2001, and Nathan instructed his subordinate to kill Gareth to ensure that the future invasion would be successful, not even yielding when the Doctor suggested that their names may just be a coincidence. Faced with no other choice, the Doctor told Gareth to unleash the trap they had set up, releasing gas that brutally killed the Sontarans. While Tegan and the Doctor congratulated Gareth, the victory was short lived, as Tegan pointed out that the TARDIS scanner had turned on, revealing a fleet of ships from the Tenth Sontaran Battle Brigade, with the Doctor telling them "[it was] only the beginning." (HOMEVID: A Fix with Sontarans) Within the space of a few hours, the Doctor and Tegan returned Gareth to his correct time-stream. (PROSE: Fixing a Hole)

Possibly future
If Nathan was correct in his assumption, then Gareth grew up to join the Earth Defence Force. becoming its leader by the time of the 2001 Sontaran invasion of Earth, which he played a major part in thwarting. (HOMEVID: A Fix with Sontarans)

Personality
If the Sixth Doctor was correct in his assumption that Gareth was like himself, then Gareth embodied traits of courage, intellect and perspicacity. Gareth also seemed to be fairly reserved, although he did have fun in making the Doctor and Tegan jump by shouting "boo" at them. (HOMEVID: A Fix with Sontarans)

Behind the scenes
Gareth Jenkins, who lived in Milton Keynes, wrote into the wish-fulfilment programme Jim'll Fix It in around 1985, to ask if he could meet Colin Baker and go inside the TARDIS; his request was approved, and A Fix with Sontarans was formed, a mini-episode wherein Gareth got to do just what he asked.

However, after the death of Jimmy Savile in 2011, the individal who hosted Jim'll Fix It, was exposed as a serial paedophile , and A Fix with Sontarans was removed from later pressings of the DVD release of The Two Doctors, which had included it since the DVD's original 2003 release. However, it was clarified by Jenkins himself that Savile had not taken an interest in him. In 2022, the Doctor Who: The Collection — Season 22 blu-ray boxset was released, including a newly-recut edition of A Fix with Sontarans, which entirely removed two minutes of footage of Savile, replacing it with a new CG scene with ADR as a new ending to the story.

As the original version of A Fix with Sontarans broke the fourth wall so thoroughly — essentially dissolving into the real world — this Wiki never considered it a valid source for writing "in-universe" articles with. It was only in coverage of PROSE: Fixing a Hole — a short story that acted as a sequel to A Fix with Sontarans and as the the thematic and conceptual concluding bookend to Tegan's journey with the Doctor — did references come to A Fix with Sontarns in valid media, albeit vaguely. Fixing a Hole notably ignored the ending of the original A Fix with Sontarans, long prior to the crimes commited by Savile came to public attention. The 2022 recut edition, as it omitted the original fourth wall breaking ending, is a valid source, however due to the ending being changed, the references to Gareth's Nan and the naming of the meson gun remain in the orignal, and thus, as invalid source articles.

Information from invalid sources
According to one account, after Gareth killed the Sontarans, Jimmy Savile entered the TARDIS, and asked the Doctor if "[Gareth] passed the test". After the Doctor confirmed so, Savile asked Gareth where he got his coat, and Gareth told him that his Nan had made it for him. Savile asked the Doctor to place a Jim'll Fix It medal over Gareth's bonce, and as the Doctor did so, he told Gareth that he was "well and truly fixed." (NOTVALID: A Fix with Sontarans)