Torgo features as the main villain in the following episodes of the classic series.
Torgo, Torgo’s Invasion of Earth, The Chase (Featuring Torgo), Torgo’s Master Plan, The Power of Torgo, The Evil of Torgo, The Day of Torgo, The Planet of Torgo, Death to Torgo, The Genesis of Torgo, The Destiny of Torgo, The Resurrection of Torgo, The Revelation of Torgo, and The Rememberance of Torgo.
He also briefly appears in a number of other episodes including The Hand Museum.
The appearance of his knees varied over time. In the earliest episodes the knees were primitive metal attachments that required manual operation by the actor. By the 1980s they were remote controlled by a stagehand, allowing the actor to concentrate on looking shifty and spouting ridiculous lines of dialogue in a halting voice.
(An actual sensible entry will probably be made later in the week)