Supercomputer

Xoanon was a supercomputer meant to guide the Mordee expedition. He eventually developed into a new, living creature and subsequently became "the most powerful computer ever built". He inadvertently became insane when the Fourth Doctor helped repair him, and became a god to the humans whose development he guided. Upon the Doctor's return to the Mordee expedition, the Doctor connected his brain with Xoanon once more. The Doctor's personality was erased and Xoanon was whole again. The Doctor then left Xoanon and the humans to their own devices. (TV: The Face of Evil)

The Xylok known as Mr Smith was identified as a supercomputer by Luke Smith (TV: The Day of the Clown) and Rani Chandra. (TV: The Nightmare Man) Clyde Langer also identified K9 Mark IV as a supercomputer. (TV: The Gift)

Behind the scenes

 * According to NOTVALID: Know Your Enemy, a TARDIS data extract suggested that the Lone Cyberman had a supercomputer fused to his cerebral cortex.