Elizabeth ("Liz") Shaw

One of the Third Doctor's companion, a Cambridge scientist recruited by UNIT's Brigadier Lethbridge-Stewart to investigate the first Nestene invasion.   She became the first assistant of the Third Doctor, whom she helped against the Silurians, the so-called Ambassadors of Death, and the forces unleased by Professor Stahlman's Inferno.  During that adventure, the Doctor met her alternate Earth counterpart, Section-Leader Shaw.  She left soon afterwards to continue her scientific career.  Her image was used by Rassilon to ward off the Third Doctor.   The Seventh Doctor gave Liz's UNIT pass to Ace.