Bessie

Bessie, also called Betsy (COMIC: Timebenders), was the Third Doctor's main mode of transport during his exile on Earth, although other incarnations of the Doctor have also used the car. A canary-yellow Edwardian roadster, she was a key part of his compensation package from UNIT, and the only specific demand he made of the Brigadier when he agreed to be UNIT's scientific advisor. (TV: Spearhead from Space) Despite being beloved by the Doctor, the car was frequently ridiculed and underestimated by the Doctor's friends. Heavily tricked out, the car's many modifications often bewildered his associates. (TV: The Dæmons, The Time Monster, Battlefield) The Brigadier in particular was dismissive of the car's abilities and, at least early on, didn't even believe it was capable of basic locomotion. (TV: The Ambassadors of Death)

Modifications
The Doctor made several modifications to Bessie during his time at UNIT. These included: an anti-theft force field (TV: The Ambassadors of Death), which magnetically trapped anyone attempting to steal Bessie; a remote control (TV: The Dæmons), with which the Doctor could steer the car from a distance, and enabling him to thwart 's attempt to escape following the events at Devil's End; and a minimum inertia hyperdrive, which allowed him to drive at breakneck speed and still come to a sudden stop without the car's occupants being tossed through the windscreen by inertia, which the brakes absorbed. The Doctor made use of this inertia absorption to overtake the Brigadier's Land Rover after Lethbridge-Stewart had declined to travel in Bessie in fear of the car's reliability. (TV: The Time Monster)

History
When he began his exile on Earth, the Third Doctor (who had just regenerated and not fully recovered) stole an antique roadster parked in front of Ashbridge Cottage Hospital to get around. He liked it and while seeing the car returned to its rightful owner, Doctor Beavis, the Brigadier said he thought he could get something like it. The original car was red, unlike Bessie, which was yellow. (TV: Spearhead from Space) As per his request, the Doctor was donated an old vehicle that he could spruce up into his working transport. It required some tuning up beneath its chassis and adjustments to get the engine working. The Doctor made these repairs in a UNIT garage where he did not wish to be disturbed. Shortly after getting the final repairs in place and attaching his personal license to Bessie, the Doctor took her out for a test drive to Wenley Moor to attend a meeting at an underground cyclotron research centre. (TV: Doctor Who and the Silurians) The Doctor claimed he named Bessie after his assistant, Liz Shaw. (COMIC: Change of Mind)

Bessie proved instrumental in capturing. When he 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. (TV: The Dæmons) Bessie was briefly pulled into Omega's universe during his attempt to capture the Doctor. (TV: The Three Doctors) Shortly after his companion Jo Grant left him and the third incarnation of the Doctor had temporarily left Earth, his fifth incarnation arrived on Earth and borrowed Bessie while helping UNIT defeat the Xaranti. (PROSE: Deep Blue)

Bessie was also abducted with the Doctor into the Death Zone, where it was heavily damaged by one of the thunderbolts that periodically rained down upon the landscape. (TV: The Five Doctors)

One of the many versions of Clara Oswald created after she entered the Doctor's time stream saw the Third Doctor driving in Bessie. She called out to him, but he didn't hear her. (TV: The Name of the Doctor)

With his waning interest in affairs at UNIT and Earth, the Fourth Doctor soon lost interest in Bessie, though he did have use for her on several Earthbound adventures with Sarah (TV: Robot, COMIC: Death Flower, Counter-Rotation, Mind Snatch, and others). He also used Bessie after Sarah was no longer travelling with him, (COMIC: The Fire Feeders) and even when Leela had joined him. (COMIC: The Devil's Mouth)

It was unclear what happened to Bessie after this early period of the Fourth Doctor's life. According to one account, it was simply in storage aboard the TARDIS, seen there as late as the Sixth Doctor's travels with Frobisher and Peri. (COMIC: Changes) Another account had it that the Brigadier had it "put into mothballs" at some point, having realised that the Doctor's visits to Earth were becoming more and more infrequent. It was brought out briefly in 1997 as the Brigadier and UNIT worked with the Doctor's seventh incarnation to battle Morgaine; it was briefly criticised by Ace, until the Doctor demonstrated its capabilities. (TV: Battlefield). The Eighth Doctor used it while defeating the Mars invasion later into 1997. (PROSE: The Dying Days)

Fancying himself an "artist," the Eleventh Doctor decided to "pimp" Bessie by hooking her up to the TARDIS matrix and turning on the random setting which transformed Bessie into a monster truck. Alice Obiefune later struggled to drive the newly transformed Bessie to save the Doctor from a group of brainwashed individuals under the control of a SERVEYOUinc representative in 1931. (COMIC: What He Wants...)

Technology
Bessie had a built in increased gravity stabiliser. (COMIC: The Vortex)

Registration
Initially, Bessie carried the registration license plate WHO 1. Whether this was intentional — possibly chosen by the Doctor as a reference to the question often asked of his name — or a coincidence is not known. By seeming coincidence, at the time of the Seventh Doctor's encounter with Morgaine, the plate had been changed to WHO 7. (TV: Battlefield) When the Eighth Doctor utilised Bessie during the 1997 invasion of Britain, a UNIT soldier reported the number plate as "Whiskey, Hotel, Oscar 8," that is, WHO 8. (PROSE: The Dying Days) After the Eleventh Doctor transformed Bessie into a monster truck, the license plate once again read WHO 1. (COMIC: What He Wants...)

Behind the scenes

 * The actual registration WHO 1 was already in use in real life by another motorist, so Bessie was actually registered under a different number plate, MTR 5. Special WHO 1 number plates were made, which were used on the car when filming on private ground or on the public highway with permission from the police.
 * A photograph of Jon Pertwee driving Bessie appears in the frame of a mirror owned by Pertwee's character, Paul Henderson, in the 1971 film . At the time of filming, Pertwee was still playing the Doctor.
 * Phil Collinson said he paid 50 pence for a ride on Bessie round a shopping centre when he was a child.
 * Model car manufacturer Corgi made a Bessie in a series of models built to commemorate an anniversary of Doctor Who.
 * The appearance of the Third Doctor on Bessie in The Name of the Doctor was archive footage taken from The Five Doctors.
 * According to the invalid source Who is Doctor Who?, the Ninth Doctor was seen trying to fix the broken down Bessie on the side of the road.