Robot Yeti

Robot Yeti were devices created by the Great Intelligence. They may have been based on living Tibetan Yeti. However, because no living Yeti were ever definitively studied, it was also possible that the robotic Yeti was the source of the myth.

Appearance
The Yeti robots were large and hairy to disguise the control spheres that provided their motive power. The spheres were hidden under a flap at the chest. Their hands, feet and eyes were the only parts not covered in fur. The hands and feet were black and bumpy. There were at least two iterations of robot Yeti. The ones encountered by the Second Doctor in Tibet were markedly bigger than the ones he encountered in England. The ones in London had better-defined hands, capable of wielding guns. The Doctor called the ones encountered in London "a sort of Mark II". (DW: The Abominable Snowmen, The Web of Fear)

20th century
The Yeti served the Great Intelligence (DW: The Abominable Snowmen), also known as the Great Old One Yog-Sothoth. (NA: All-Consuming Fire) A non-corporeal entity, the Great Intelligence, took over the body of Padmasambhava, the lama of Det-Sen Monastery. The Great Intelligence created the robot Yeti in order to conquer the Earth. The Yeti were initially a ruse to scare off curiosity seekers; later, they became more of an army serving the Great Intelligence. These robots were similar in appearance to what Edward Travers called "real" Yeti.

The Second Doctor, a friend of Padmasambhava's, arrived in the Himalayas 1935 with his companions Victoria and Jamie. Along with the explorer Professor Edward Travers, they put an end to the Great Intelligence's plan, at least for a time. (DW: The Abominable Snowmen)

More than forty years later, a formerly non-functioning Robot Yeti on display in London was reactivated by a control sphere. The robots then covered London in webbing, forcing the evacuation of the populace. Later, in the Underground, Alistair Gordon Lethbridge-Stewart and his troops attempted to stop them. (DW: The Web of Fear) This event gave impetus to the formation of UNIT. (DW: The Invasion)

Lethbridge-Stewart again encountered a Yeti on Gallifrey, left over from Rassilon's game. On this occasion, the Second Doctor maddened it with a firework, and the resulting rock fall prevented any further interaction with it. (DW: The Five Doctors)

From 1970 to 1985, the Great Intelligence once more attempted to take over Earth with the help of the former companion of the Second Doctor, Victoria Waterfield, who it had taken over, and, once more, the Yeti. The Brigadier and Sarah Jane Smith defeated them. (RP: Downtime)

21st century
A Yeti sidearm was removed from the Hub, the underground HQ of Torchwood 3, following the Hub's destruction. It was was then delivered to the CIA Special Operations Division who went rogue and stole the shipment. (TWN: The Men Who Sold the World)

Other encounters
A group of Yetis were put in the Doctor's TARDIS by the Doctor to battle the Graak. (VG: Destiny of the Doctors)

Alternative timelines
In an alternate timeline created by the Black Guardian where the First Doctor never left Gallifrey, and became Lord President, the Yetis were one of many forces that invaded Earth, and fought over the planet with invaders of various alien races. This timeline was destroyed when the Seventh Doctor retrieved the Key to Time. (DWM: Time & Time Again)

Continuity

 * Because no clear pictures exist of the supposed "real" Yeti seen at the end of The Abominable Snowmen, direct comparison of the Mark I and "real" Yetis, as televised, is impossible. However the novelisation does afford such a comparison: "It was taller and less bulky. The fur was longer and silkier, and had a more reddish tint. Above all, the face was different, rather like that of a lemur, with dark, soft eyes." Nevertheless, it is extremely unlikely that the brief wide shot that was included in the episode as broadcast would have been able to convey this level of detail. Indeed, this is an instance where the novelisation may be said to actively contradict the televised episode. Since episode six is missing, it is impossible to judge the reliability of this description.''
 * The date of the second Yeti invasion is the point at which the UNIT dating controversy begins. The script of episode two of The Web of Fear says that the events of Snowmen took place "in 1935" which is in turn said to be "over forty years ago". This means that "Web" has to take place no earlier than late 1975. Since Lethbridge-Stewart is only a colonel in Web, it means his next appearance in The Invasion, and all the subsequent ones must take place even later than 1975, well after Tom Baker had begun to play the Fourth Doctor in real life. However, episodes made under John Nathan-Turner, and particularly Mawdryn Undead, indicate that the UNIT stories all took place in more or less the year they were broadcast. Also, the semi-official UNIT website gives the date of the incident as 1968, the same year The Web of Fear aired. Hence, the Tenth Doctor eventually refers to his time working for UNIT as vaguely happening in the 1970s or 1980s. (DW: The Sontaran Stratagem)

Appearances in unmade stories
The Yeti would have reappeared in The Laird of McCrimmon, a story abandoned because of the Yetis' creators dispute with the BBC. This story would have seen the writing out of the character of Jamie McCrimmon. The Yeti would also have also appeared briefly in the planned 30th anniversary special The Dark Dimension in a scene deliberately echoing The Web of Fear.