Tibetan Yeti, also known as Abominable Snowmen, were anthropoid creatures that dwelt in the Tibetan Himalayas on Earth.
Species
By 1984, three species of Yeti were formally identified and classified: "Mih-teh" and "Dzu-teh", which were large apes, and "Yeti Traversii", found by Edward Travers, was more bear-like and very timid. In 1984, the London Zoo had a female Yeti Traversii named Mahamaya, which was successfully bred with a male from Peking. Their child was named Margaret for the Prime Minister Margaret Thatcher, whom she bit at a photocall. (PROSE: Downtime)
History
Little was known about them, except that they were large, furry, probably semi-sapient humanoids. They were timid, rarely approaching travellers, and most in the western world believed them mythical
The First Doctor, Dodo Chaplet and Steven Taylor encountered a pack of Yeti near the Det-Sen Monastery. Dodo became enamoured with them and used them to help defeat a set of bandits. (AUDIO: The Secrets of Det-Sen)
Professor Travers went on an expedition to find them in 1935 to prove that they actually existed. After an adventure with the Second Doctor and the Robot Yeti, Travers believed he had spotted one and went off in pursuit. (TV: The Abominable Snowmen) However, according to most accounts, this Yeti turned out to just be a surviving robot. (PROSE: Times Squared) Capturing it, Travers brought it back to London, where he showed it to the War Department. The report was not taken very seriously at the time, but, by 1963, had been reappraised following the British Rocket Group's unambiguous discovery of extraterrestrial life in 1953 (which was covered up for the general public, but widely circulated in the higher spheres of government); it thus played a part in the creation of a government agency devoted to defending against hostiel extraterrestrial incursions, (PROSE: Background) the Intrusion Counter-Measures Group. (TV: Remembrance of the Daleks) Years later, Travers did not appear to possess any proof of the species' existence. (TV: The Web of Fear)
Decades later, a team of monster hunters attempted to photograph the elusive Yeti and were captured by the Great Intelligence responsible for the creation of the Robot Yeti. Lama Gampo, a monk who had sworn to protect the world from the Intelligence, blew a great horn and called the real Yeti, who howled in response and descended the mountains to fight against their robotic counterparts. (COMIC: Yonder... The Yeti)
In 1984, the Yeti was formally classified. (PROSE: Downtime)
Possible sightings
A Yeti was in the Death Zone on Gallifrey when several incarnations of the Doctor were summoned there by Borusa during his quest to claim immortality from Rassilon. (TV: The Five Doctors)
During their journeys in the 20th century Bea Nelson-Stanley and her husband Edgar saw young Yetis frolicking in the snow. Bea thought they were wonderful. (PROSE: Eye of the Gorgon) According to Bea, the Sultan of Ishkanbar had also seen a Yeti. (TV: Eye of the Gorgon)
The Museum of Things That Don't Exist had nine different varieties of Yeti that all supposedly didn't exist. However, the exhibits weren't known for their accuracy. (PROSE: The Taking of Planet 5)
Behind the scenes
A real Yeti on TV?
The question of whether there are "real" Yetis in the Whoniverse is not possible to definitively answer just from televised episodes alone, although it appears to have been implied as indicated below.
One may have appeared at the end of The Abominable Snowmen, but the script is considerably unclear as to this point. According to production records of the now-wiped serial, the supposed "real" Yeti would only have been briefly glimpsed in a long shot, and it may have been depicted with a slightly "slimmed-down" version of the robot Yeti costumes. Whether that would have been enough for viewers to actually detect a difference between the "real" and robotic Yeti is unknown. Certainly, production records indicate that a close-up of a "real" Yeti has never been shot for televised Doctor Who.
Whatever the original intent of The Abominable Snowmen, the 1995 short story Background and the 2016 Lethbridge-Stewart novel Times Squared both state that the Yeti spotted by Travers at the endof The Abominable Snowmen was simply yet another robot. Meanwhile, however, the Target Books novelisations Doctor Who and the Abominable Snowmen and Doctor Who and the Web of Fear definitely refer to "real" Yetis in ways that the televised episodes don't. The Snowmen novelisation gives a vivid depiction of the difference between living and robotic Yetis, but this description is at variance with what viewers would have been able to detect in a monochromatic long shot on television. And, despite the fact that Travers recalls the "real" Yeti in the novelisation, the Fear script never mentions "real" Yeti whatsoever. It even makes it possible for viewers to assume that the robot Yeti he returned to London was in fact the "real" Yeti he'd been chasing at the end of Abominable (which the suggestion made in Background).
A possible image of the "real" Yeti of Abominable does exist. However, as it's a telesnap, and all location work for the serial was done in a mere six days, it's entirely possible this image didn't come from episode six at all. There's a sequence in episode four where a lone robotic Yeti climbs a mountain, and the surviving telesnap could in fact have documented that sequence, instead. It could also be an outtake of a Yeti-portrayer falling down the mountain, since it is known that the Yeti-portrayers were constantly slipping on muddy patches during the shoot. Even if it is real, the shot in no way clearly distinguishes its subject from a robotic Yeti.
As of 2017[update], the clearest surviving documentation of "real" Yetis in the Doctor Who universe is the Doctor Who Magazine comic strip, Yonder... The Yeti.
Information from invalid stories
According to Strange to Tell... According to the Daleks (a comic from The Dalek World which, due to not having a plot to speak of, is not considered a valid source on this Wiki), the true Yetis are in fact Dalek mutants who, having crashed their saucer in the Himalayas in the year 141, found they could survive beyond their casing in the rarified atmosphere and sub-zero temperatures.