Lupton was a human from 1970sEarth who, having lost his job when a takeover of the firm he worked for resulted in his redundancy, sought power and revenge. He worked on developing his mental abilities at K'anpo Rimpoche's meditation centre, where he was contacted by one the Eight Legs of Metebelis III to help them find a blue crystal that the Third Doctor had taken. He was later taken to Metebelis III and began to turn against the Eight Legs, but was arrested by their guards.
Lupton later insulted the Eight Legs by calling them "superstitious fools", as well as "spiders" — the use of which the Eight Legs had forbidden. He then tried to attack the Queen, but the Queen killed Lupton before he could strike her. (TV: Planet of the Spiders)
Behind the scenes
According to The Doctor's Lives and Times, his first name was Rex and he had been retired from his post as Sales Director at Chatfield Electronics after it merged with Magpie Electricals.