Robot Yeti

The Yeti are both a species and type of robot, both of which can be found in the Himalayan mountains, particularly in Tibet. (DW: The Abominable Snowmen)

Appearance
Little is known about the Yeti creature, as they are naturally timid. They seem to be large, hairy, humanoid creatures. They are generally thought to be myths by Humans. (DW: The Abominable Snowmen)

The Yeti robots appear as large, hairy, bipedal robotic forms, which disguise the spherical mechanism that provides its motive power. They serve the Great Intelligence, a disembodied consciousness. (DW: The Abominable Snowmen, The Web of Fear)

History
The Yeti were originally designed by the Great Intelligence in the guise of real Yeti, in order to scare of curiosity seekers in 1920s Tibet, but later in 1968 to form an army to serve the Intelligence. Both attempts to invade were thwarted by the Doctor. (DW: The Abominable Snowmen, The Web of Fear) The latter attempt was one of the events which caused the formation of UNIT. (unit.org.uk)