Doctor Who: The Newbies Guide
This is the fourth and final story in Season 7.
The Third Doctor has white hair, a large nose, and tends to dress as a society dandy. He has a love of technology, historical name-dropping, and vehicles. In The War Games the Doctor's people (the Time Lords) sentenced him to exile on Earth. In Spearhead from Space, he was appointed as scientific advisor to UNIT.
Brigadier Lethbridge-Stewart is the commanding officer of the United Nations Intelligence Taskforce (UNIT). He worked with the Second Doctor to defeat threats to Earth on two occasions (in The Web of Fear and The Invasion. In Spearhead from Space, he teamed up wiih the Third Doctor to prevent an invasion by the Nestene and the Autons. During that story he persuaded the Doctor to work as his scientific adviser.
Elizabeth "Liz" Shaw is a brilliant scientist who was hired as UNIT's scientific adviser in Spearhead from Space. She was initially sceptical about the alien threats that UNIT fights.
Sergeant Benton is a UNIT officer. He previously worked with the Doctor in The Invasion and The Ambassadors of Death
Recurring and Historical Characters
The United Nations Intelligence Taskforce (UNIT) is an organisation devoted to protecting Earth from extra-terrestrial threats, In The Invasion, the second Doctor teamed up with them to prevent an invasion by the Cybermen. In Spearhead from Space, the Doctor became their scientific advisor.