Doctor Who
Baker made his Doctor Who debut as the antagonistic Time Lord Commander Maxil in Arc of Infinity (1983), who notably shoots the Fifth Doctor (Peter Davison) in the cliffhanger to "Part One". Davison later joked that Baker was going after his job. Baker was unavailable to reprise the role in "The Five Doctors" (1983); during the filming of that episode, Davison informed producer John Nathan-Turner that he was leaving Doctor Who. Nathan-Turner had initially chastised Baker for upstaging Davison with his "arch" performance, but after encountering Baker entertaining guests at the wedding of a mutual friend, he remarked to his partner Gary Downie "I think I may have found my new Doctor". Baker was offered the part on 10 June. Baker was delighted as he had assumed there was an "unwritten rule" that playing a different character on the series prohibited him from playing the Doctor. He had been a fan of the series since the 1960s, and considered applying for the lead role when Fourth Doctor actor Tom Baker left in 1980. His casting was announced on 19 August 1983, and the Sixth Doctor first appeared in the final moments of The Caves of Androzani (1984).
Baker was keen to emphasise the Doctor's alien behaviour, and the intention was for his brash and arrogant incarnation to mellow over time. Baker suggested a dark costume which would allow his Doctor to go unnoticed; ironically, he was dressed in a multi-coloured coat designed to be "totally tasteless". Neither fans nor critics reacted favourably to the Sixth Doctor's debut. His first full story The Twin Dilemma (1984) is often regarded as one of the worst in the history of the series. The new Doctor's unlikeability was established when, in a post-regeneration mood swing, he tries to strangle his companion Peri Brown (Nicola Bryant)—a scene widely condemned for its shock value. In 2010, PopMatters called his first appearance "just out-and-out dislikable, showcasing a hubris and harshness that was heretofore unseen in the Doctor's emotional canon." Due to concerns over season 22's overtly violent tone and lack of humour, production of the planned 1986 season was suspended in February 1985. Michael Grade, the controller of BBC1, personally disliked Doctor Who and criticised its outdated production values. He reportedly described Baker's performance as "absolutely god-awful". During the 18-month hiatus, Baker and Bryant starred in the Doctor Who radio drama Slipback (1985). Both actors also contributed their vocals to "Doctor in Distress" (1985), a charity single produced to raise money for the National Society for Cancer Relief and support the series' return.
In September 1986, Doctor Who returned to television, with a reduced episode count, for season 23, known collectively as Trial of a Time Lord. The season's story arc, which involved the Doctor on trial for his crimes against Time Lord society, was a meta-textual reference to the series itself being "on trial". Grade and Jonathan Powell (BBC's Head of Series and Serials) took the new season's disappointing ratings as justification that Baker did not appeal to the public, and instructed Nathan-Turner to recast the Doctor. Davison later suggested that the executives wanted Nathan-Turner to resign as producer by forcing him to change the Doctor. In 2021, Toby Hadoke described Baker as "a fall guy for all the criticisms levelled at the show, which had nothing to do with him".
On 29 October, Nathan-Turner informed Baker over the phone that the Sixth Doctor would be replaced. Baker had signed a four-year contract, as the BBC initially hoped he would stay on for longer than Davison's three-year stint, but his two-season tenure as the Doctor was the shortest of any actor at that point. Baker was upset as there was much he still wanted to do with the role. Powell offered Baker a four-part story concluding in his character's regeneration. Baker argued for one more complete season, as he did not want to commit himself to only two weeks' work when he should be seeking out regular work elsewhere. Baker never heard back from Powell. The new Seventh Doctor, Sylvester McCoy, played the injured Sixth Doctor in the opening minutes of season 24's debut serial Time and the Rani (1987), his face hidden by visual effects as the regeneration process occurs. In a 2019 interview, Baker expressed regret for not returning for a regeneration scene, stating that he was feeling "hacked off" and not thinking about the fans.
From June to August 1989, Baker succeeded Jon Pertwee as the Doctor in the stage play Doctor Who – The Ultimate Adventure. Baker reprised the role on television for the first time in the 1993 Children in Need charity special Dimensions in Time, alongside every surviving Doctor. In 1997, he provided dialogue for the BBC video game Doctor Who: Destiny of the Doctors. Baker and McCoy reprised their roles for a 2003 Dead Ringers Children in Need sketch where the Sixth and Seventh Doctors compete against alien foes on the game show Weakest Link. In 2003, Baker appeared on Top Gear in character as the Doctor. He competed in a lap of the Top Gear track against various drivers dressed as a Klingon, a Cyberman, a Dalek, Darth Vader and Ming the Merciless.In 1999, Baker appeared alongside Davison and McCoy in The Sirens of Time, the first of Big Finish Productions' licensed Doctor Who audio dramas. Baker regularly played the Sixth Doctor in Big Finish's Main Range series until its conclusion in March 2021, with the character's stories continuing in the ongoing series The Sixth Doctor Adventures. Big Finish gave Baker the chance to continue the Sixth Doctor's long-term character arc, which has rehabilitated the character's reputation. In a 2001 poll conducted by Doctor Who Magazine, Baker was voted the Best Audio Doctor. The 2015 audio drama The Last Adventure, which depicts the Sixth Doctor's final adventure before his regeneration, afforded Baker the send-off he was denied on-screen. Baker reprised the role of Commander Maxil in the Gallifrey episode "Appropriation" in 2006. In 2022, he played an alternate version of the Doctor ("the Warrior") in the Doctor Who Unbound series, and an elderly future version of the Doctor ("the Curator") in The Eighth Doctor Adventures.
In the 2022 television special "The Power of the Doctor", Baker returned for a cameo appearance alongside Davison, McCoy and Paul McGann as a manifestation of the Thirteenth Doctor's subconscious. Baker reprised his role as the Sixth Doctor in Tales of the TARDIS (2023) to mark Doctor Who's 60th anniversary.
Baker has written various published Doctor Who short stories, including "The Deal" (1991), "A Wee Deoch an ...?" (1991), "A Tourist Invasion" (1992) and "Interstitial Insecurity" (2019), all featuring the Sixth Doctor. In 1994 he wrote the comic story The Age of Chaos. He wrote and read the short story audiobook "The Wings of A Butterfly" for Big Finish. He presented the home video releases Cybermen – The Early Years and The Colin Baker Years. At Riverside Studios on 4 September 2011, Baker accepted the post of Honorary President of the Doctor Who Appreciation Society.
Baker starred in the comedy short film The Five(ish) Doctors Reboot (2013) as a fictionalised version of himself who assists Davison and McCoy in sneaking into the production of the 50th anniversary special "The Day of the Doctor". Since 2023, Baker hosts the Big Finish-produced podcast Into the TARDIS, which showcases fan-favourite Big Finish stories.