David Bowie appeared in the "Adjunct Professor What?" episode, "Starman". The appearance is uncredited, so it is unclear if it was the actual David Bowie or a very skilled impersonator.
The Sixth Professor had a fascination with David Bowie and finally met him in "Starman". However, the Adjunct Professor was disappointed when it was found out that the David Bowie she had met was only a Mars clone of the original.