The Cybernetic Personality Matrix was created by Gallifreyan cyberneticists in an attempt to create Model 51 TARDISes with anthropomorphic personalities and sentience.
Their original intent when developing the Model 51s was that Time Lord pilots would become redundant, and TARDISes could fly themselves, at least on simple observational missions. This idea was gradually abandoned in favour of programming the Matrices with helpful "co-pilot" personalities who could act as friends and equal partners to the pilot.s
However, even this hope proved ill-founded. Due to some basic design flaw which the engineers never pinpointed, the Model 51s' artificial personalities were unstable, constantly shifting from emphasising one personality trait to another — cycling through "balanced", "helpful", "stubborn", "protective", "sullen", "cautious", "complaining", "bossy", "hostile", "practical joker", "slow", "haughty", and "argumentative" spells at the slightest disturbance. (GAME: "TARDIS Model 51 Personalities" [+]Part of The Iytean Menace, J. Andrew Keith, The Doctor Who Role Playing Game (FASA, 1985).)