Bessie

The Third Doctor's main mode of transport, during his exile on Earth, Bessie was a canary-yellow roadster, acquired by the Brigadier for the Doctor's use as part of the exiled Time Lord's agreement to assist UNIT in its efforts to protect the planet. The Doctor made several modifications to Bessie during his time at UNIT. These included an anti-theft force field ("The Ambassadors of Death") which magnetically trapped anyone attempting to steal Bessie, a remote control ("The Daemons"), with which the Doctor could steer the car from a distance,  and a minimum inertia hyperdrive ("The Time Monster") which allowed him to drive at break neck speed and still come to a sudden stop without him or his passengers being sent through the windshield by inertia, which the brakes absorbed.

Bessie proved instrumental in capturing the Master. As the Time Lord criminal attempted to steal the Doctor's car and make good his escape following the events at Devil's End, the Doctor used his remote control to steer the Master back to the waiting UNIT soldiers, who took him into custody. Bessie was briefly pulled into Omega's universe during his attempt to capture the Doctor ("The Three Doctors"). The car was also abducted along with the Third Doctor into the Death Zone, where it was heavily damaged by one of the thunderbolts periodically reigned down upon the place. Presumably it was Rassilon who returned the car to Earth at the conclusion of this adventure ("The Five Doctors").

Upon the Fourth Doctor's departure from Earth, Brigadier Lethbridge-Stewart had it "put into mothballs". It was brought out briefly in the 1990s as the Brigadier and UNIT worked together with the Seventh Doctor to battle Morgaine ("Battlefield")