Baker portrays the Fourth Doctor as a whimsical and sometimes brooding individual whose enormous personal warmth is at times tempered by his capacity for righteous anger.

His initial companions were the journalist Sarah Jane Smith (Elisabeth Sladen), who had travelled with his previous incarnation, and Surgeon-Lieutenant Harry Sullivan (Ian Marter) of UNIT.

His later companions were the warrior Leela (Louise Jameson), robotic dog K9 (John Leeson and David Brierly), female Time Lord Romana (Mary Tamm and Lalla Ward), teen mathematical genius Adric (Matthew Waterhouse), teen alien aristocrat Nyssa (Sarah Sutton), and Australian flight attendant Tegan Jovanka (Janet Fielding).

[2] The Fourth Doctor's eccentric style of dress and speech – particularly his trademark look of wearing a long scarf and having a fondness for Jelly Babies – made him an immediately recognisable figure and he quickly captivated the viewing public's imagination.

The producer of Baker's early seasons, Philip Hinchcliffe, stated that the Fourth Doctor's bohemian appearance and anti-establishment style appealed to older, college-age students.

One writer in the Daily Mail complained in early 1975 that, "Mr. Baker makes Doctor Who look like Harpo Marx let loose from Horse Feathers."

The Doctor travels with journalist Sarah Jane Smith, whom he had befriended prior to his regeneration, and, for a time, with UNIT Surgeon-Lieutenant Harry Sullivan.

To avoid execution, the Doctor invokes an obscure law and declares himself a candidate for the office, giving himself the time he needs to prove his innocence and expose the real culprit.

During his previous visit, he had accidentally imprinted his own mind on a human colony ship's powerful computer, Xoanon, leaving it with multiple personalities.

The two Gallifreyans travel to a variety of planets, encountering strange and unusual allies and enemies, gathering the six segments and defeat the equally powerful Black Guardian, who sought the Key for himself.

Perhaps because of this, the Doctor begins frequently over-riding the machine, first travelling to Paris for a holiday, only to get caught up in an alien scheme to steal the Mona Lisa (City of Death).

The Doctor decides to travel to Earth to scan a real Police Box as part of a plan to repair the "Chameleon Circuit", the shape-changing mechanism in the TARDIS.

As the Doctor prepares to travel to the planet Logopolis to get the Chameleon Circuit fixed, Tegan Jovanka appears in the console room (having previously gotten lost in the corridors of the TARDIS).

The Master agrees to help the Doctor stop the spread of Entropy by adapting the Pharos Project radio telescope on Earth so that they are able to reopen the CVEs.

The Fourth Doctor also had a small cameo at the beginning of Dimensions in Time, warning his Third, Fifth, Sixth and Seventh incarnation to watch out for the Rani.

Imposingly tall, with eyes that seem to constantly boggle, a mass of curls for hair and prominently displayed teeth, the Doctor favours an outfit that usually consists of a white shirt, waistcoat, cravat, trousers, a frock coat (with pockets containing a seemingly endless array of apparently useless items that would nevertheless suit the Doctor's purposes when used), a fedora and, most famously, his impractically long, multi-coloured scarf, which was apparently knitted for him by Madame Nostradamus (whom he refers to as a "witty little knitter").

According to both the creators of the show and Baker, the character's look was originally based on paintings and posters by Henri de Toulouse-Lautrec of his friend, Aristide Bruant, a singer and nightclub owner whose trademark was a black cloak and long red scarf.

[8] When John Nathan-Turner became the show's producer in Baker's last year, the Fourth Doctor was the first to sport an item of clothing adorned with question marks as a motif, in this case, above the points on his shirt collars.

The duo of writer/script editor Robert Holmes and producer Philip Hinchcliffe consciously tapped into horror icons like mummies (Pyramids of Mars) and Frankenstein (The Brain of Morbius, Robot), vampires (State of Decay) and Jekyll and Hyde (Planet of Evil), and even transformation (The Ark in Space, The Seeds of Doom) and various themes like alien abduction.

With the cast and crew suffering from burnout and lack of resources, the season finale The Invasion of Time (1978) was completed largely by virtue of it having been written to make use of preexisting sets, props, and costumes.

Bidmead asked a pair of writing friends to come up with what would be the second story of the season, Meglos (1980), which ended up being regarded as one of the weakest shows in the series' history up to that point.

The Fourth Doctor also appears in Sarah Jane's flashback in The Mad Woman in the Attic, via footage taken from The Hand of Fear.

For audiences in the United States, who saw the show only in syndication (mostly on PBS), Tom Baker was the incarnation of the Doctor who is the best known, since his episodes were the ones most frequently broadcast stateside.

The first four seasons of these Time Life distributed stories added narration by Howard da Silva at the beginning and end of each episode.

In the computer game Hugo II, Whodunit?, the player can save the Fourth Doctor from a Dalek in return for his sonic screwdriver.

He is frequently impersonated by impressionist Jon Culshaw on the radio and television series Dead Ringers, who also voiced the Doctor for the Big Finish audio The Kingmaker.

Archival footage of the Fourth Doctor's first title sequence was used in the Family Guy episode "Blue Harvest" to parody hyperspace from Star Wars.

[17] In 1979 and 1980, Tom Baker played the Fourth Doctor (alongside Lalla Ward's Romana) in a series of four television commercials for Prime Computer.

[18] Disliking the scripts he was given, Baker agreed to film the advertisements only if he could rewrite them himself, and added a scene where the Doctor follows the computer's instruction to marry Romana.

[20] Tom Baker also recorded narration, in character as the Fourth Doctor, for a 1976 audio release of Genesis of the Daleks, which was subsequently re-issued by the BBC on cassette and CD as a radio drama.