Gillian Who

Gillian (PROSE: Beware the Trods!) and her brother John were siblings. According to some accounts, they were the grandchildren of the Doctor and travelled with him during his first and second incarnations. (COMIC: The Klepton Parasites to COMIC: Invasion of the Quarks) According to other accounts, they never existed, but were either the dreams of the Doctor, (COMIC: The Land of Happy Endings) or the creations of the Master of the Land of Fiction. (PROSE: Conundrum)

Nature & origins
Although most accounts held that John and Gillian were real, corporeal beings, (COMIC: The Klepton Parasites, Guests of King Neptune) some accounts suggested that the two never actually travelled with the real First Doctor; one suggested that the "Dr. Who" who travelled with his grandchildren existed in the Land of Fiction. While visiting, the Seventh Doctor encountered a "John" and "Gillian" who claimed he was their grandfather in whose company they had fought the Kleptons and the Trods. They tried to make him remember that his name was Dr. Who, to which he flatly replied with denial. When they pressed further and asked if he remembered them, he said that he didn't. (PROSE: Conundrum)

Another, unrelated account stated that the Eighth Doctor had dreams in which he had adventures with John and Gillian. These dreams helped the Time Lord unwind by suggesting a less complicated reality where "villains are naughty, not evil", "people never die" and "promises are never broken". However, despite the second claim, the Doctor, in the dream, was seen to intentionally destroy a number of apparently sentient robots. After one such dream, the Doctor awoke refreshed and re-energised. (COMIC: The Land of Happy Endings)

In yet another account, John and Gillian did indeed physically exist and travel with the Doctor, but they were mathematically-computed simulacra given reality by the TARDIS based on the Doctor's wishes. They were only two of "thousands" of companions whom the Doctor had created out of thin air, perfect and unchanging, to travel at his side without fear of death, in an effort to avoid responsibilities and anxiety. These evading techniques led to the creation of a psychic entity known as the Five O'Clock Shadow, whom the Doctor would later escape by using the same TARDIS functionality to give life to perfectly angst-free versions of himself and Susan. (PROSE: The Five O'Clock Shadow)

Entering the TARDIS
According to one account, John and Gillian first met their grandfather, an old man with long white hair who called himself "Dr Who", in 1960s England, (COMIC: (PROSE: The Klepton Parasites) their home time. (COMIC: Nostalgia Corner) They knew he was some kind of inventor, but had evidently never seen him or travelled with him when they found the TARDIS in an empty yard. They entered and he acknowledged them as John and Gillian. During their visit, John touched a button on the console and the TARDIS took them to the 30th century, where they discovered the Thains were being invaded by the Kleptons. They helped the Thains repulse them, then followed the Kleptons back to the Klepton city and destroyed it, killing the Kleptons and their leader, Klepton One. (COMIC: The Klepton Parasites)

Travels with the First Doctor
John and Gillian travelled subsequently with Dr Who on many adventures, fighting Ixa, (COMIC: The Therovian Quest) Anastas Thrax, (COMIC: The Hijackers of Thrax) Zarka, (COMIC: On the Web Planet) the Gyros, (COMIC: The Gyros Injustice) Gritog, (COMIC: Prisoners of Gritog) the Pied Piper, (COMIC: Challenge of the Piper) more Kleptons, (COMIC: Prisoners of the Kleptons) the Caterpillar Men, (COMIC: The Caterpillar Men) several giant lizards, (COMIC: Lizardworld) the robots of Bellus, (COMIC: The Ordeals of Demeter) a giant shark, (COMIC: Shark Bait) the Demon Magician, (COMIC: A Christmas Story) a group of Space Rebels, (COMIC: Space Station Z-7) the black scorpi, (COMIC: Plague of the Black Scorpi) the Trods, (COMIC: The Trodos Tyranny, Return of the Trods, PROSE: Beware the Trods!) and their leaders MacTaggart (COMIC: The Trodos Tyranny) and the Master of the Trods, (COMIC: Return of the Trods) the automated defences of Gemino City, (COMIC: The Secret of Gemino) the Gorgon, (COMIC: The Gaze of the Gorgon) Zentor, (COMIC: The Haunted Planet) the emperor of Zerox, (COMIC: The Hunters of Zerox) the Professor, (COMIC: The Underwater Robot) the Ulks of Int, (COMIC: Deadly Vessel) a group of giant birds, (COMIC: Kingdom of the Animals) a Klondite (COMIC: The Galaxy Games) and the Master Race, (COMIC: The Experimenters) as well as meeting Colonel Roberts and Major Simms, (COMIC: Moon Landing) the Go-Rays, (COMIC: Enter: The Go-Ray) a dodo (COMIC: The Didus Expedition), Neptune, (COMIC: Guests of King Neptune) and William Tell.

All in all, the First Doctor spent at least 25 years trying to get John and Gillian back home, during which time the two youngsters barely aged — though by the 25th year of his travels with the Doctor, John was starting to shave. (PROSE: Nostalgia Corner)

Travels with the Second Doctor
The Doctor parted company from them, but reunited with them in his second incarnation. From their perspective, little time had passed. They resumed their adventures and fought The Extortioner, (COMIC: The Extortioner) the Daleks, (COMIC: The Trodos Ambush, The Doctor Strikes Back, The Exterminator, Jungle Adventure, Attack of the Daleks) the Zagbors, (COMIC: The Zombies) the Master of Spiders, (COMIC: Master of Spiders) a renegade gun crew, (COMIC: Barnabus) the witches (COMIC: Return of the Witches, The Witches) and their leader the Grand Witch, (COMIC: The Witches) the Cybermen, (COMIC: Masquerade, The Time Museum, The Coming of the Cybermen, Flower Power, Cyber-Mole, The Cyber Empire) more Trods, (COMIC: Pursued by the Trods, PROSE: Beware the Trods!) the band manager of the Electrodes, (COMIC: The Electrodes) a mad scientist, (COMIC: The Monsters from the Past) an unnamed tribe, (COMIC: The TARDIS Worshippers) Arborge Quince, (COMIC: Space War Two) the Mahadi, (COMIC: Egyptian Escapade) the enemy power, (COMIC: The Faithful Rocket Pack) the sabre-toothed gorillas, (COMIC: The Sabre-Toothed Gorillas) the Dyrons, (COMIC: The Dyrons) a group of space pirates, (COMIC: Dr. Who and the Space Pirates) the Criminal (COMIC: Car of the Century) and the Comedian until they reached their teen years, when the Doctor enrolled them in university on Zebadee to keep them safe from the Quarks. (COMIC: Invasion of the Quarks)

Later life
John eventually became a professor and wrote a memo on the dangers of the Trods to Colonel Marc Forest of Special Space Security. At this time, John styled himself "Professor John Who". (COMIC: Beware the Trods!)

Personalities
John could be known to be rather protective of Gillian, growing upset when she was accidentally left behind when he and the Doctor returned to the TARDIS. (COMIC: The Ordeals of Demeter)

Behind the scenes

 * It does not appear that John and Gillian had met the Doctor before the comic story The Klepton Parasites, although they were aware of his existence and the Doctor's comment upon their arrival implies that he was expecting them. Nothing was ever revealed about their lives before meeting him, aside from The Five O'Clock Shadow's retcon that they had had no prior life, instead being brought into existence via some sort of Block Transfer Computation by the Doctor to stave off his anxiety and loneliness.
 * The characters of John and Gillian were created for the Doctor Who comic strip in lieu of using (and paying license fees for) any of the companions from the television series. From the start, Polystyle Publications' rights to use Doctor Who in comic strip form allowed them to use only the title of the television series, the TARDIS and a likeness of William Hartnell.
 * At the conclusion of the comic story The Monsters from the Past, Gillian shoots the villain dead, making her one of the few sympathetic, recurring characters other than Leela, Romana I and UNIT personnel to be shown killing, prior to the BBC Wales era.
 * In the novella Time and Relative by Kim Newman, Susan Foreman has friends at Coal Hill School named John Brent and Gillian Roberts, named after John and Gillian from TV Comic.
 * John and Gillian, in their first appearance, lived in then-present-day England, and knew of their grandfather as an inventor. This suggests that the story was placing itself in the framework where the Doctor was a human being, and thus John and Gillian were implicitly humans as well; unlike Susan on television, they never displayed any alien knowledge or characteristics. In light of it later becoming established continuity that the Doctor was a Time Lord (or otherwise nonhuman), John and Gillian are thus recasts as, at the very least, part-Gallifreyan hybrids; their reappearance in 1988's Nostalgia Corner depicted them as aging at a slowed rate, much like the Doctor and Susan, but stopped shy of calling them Time Tots outright.