Cailleach: Very real Druidic goddess, alias of alien criminal, CESSAIR of DIPLOS (5C).
Caleb: Warrior of the SEVATEEM who became leader after the death of Andor (4Q).
Callufrax: Planet destroyed by ZANAK.  In reality a segment to the KEY TO TIME (5B).
Cameca: Aztec lady with whom the First Doctor flirted in order to find his way back to the TARDIS (F).
Camilla: Formerly known as Navigation Officer Lauren Macmillan of the Earth ship Hydrax.  Drawn into E-SPACE by the GREAT VAMPIRE, she became one of the immortal vampire rulers of a local planet (along with AUKON and ZARGO).  She died when the Doctor destroyed the Great Vampire (5P).
Campbell (David): Earth freedom-fighter against the DALEKS.  He married SUSAN, the First Doctor's granddaughter (K).
Capitol: City of the TIME LORDS (4P, 4Z).
Captain: Ex-pirate and apparent master of ZANAK, whose Bridge he designed.  In reality a pawn of its Queen, XANXIA, who controlled his Cyborg half and killed him when he tried to revolt (5B).
Canis: Tigellan woman who helped the Doctor against MEGLOS.  She wanted her people to reclaim their surface (5Q).
Carrington: Ex-astronaut of MARS PROBE 6.  Promoted General of the Space Security Department, he attempted to start a war between the 'radioactive Martians' he blamed for the death of his companions, and Earth (CCC).
Carstairs: Lieutenant in the British Army during the First World War.  He was a victim of the War Games (ZZ).
Castellan: Title given to the head of Gallifreyan security (4P, 4Z).
Catherine de Medici: She ordered the ST BARTHOLOMEW'S DAY MASSACRE (W).
Cavemen: Encountered by the First Doctor, whose companion Ian gave them the secret of fire (A).
Caven: Notorious Space Pirate (YY).
Celestial Intervention Agency: Secret organisation of the TIME LORDS which intervenes in the Universe's affairs when deemed necessary.  The Doctor has been its unwilling agent (4P).
Celestial Toymaker: Mysterious entity who looks like a happy mandarin and forces space travellers to play his games - or die.  He was defeated by the First Doctor (X).
Cerebretion Mentor: Device used by the CYBERMEN in their invasion of Earth (VV).
Cessair: Real name of Vivien FAY, alien criminal from DIPLOS (5C).
Chameleons: Race who lost their identities in a nuclear war.  They were discovered and defeated by the Second Doctor while in the process of taking over unsuspecting Humans (KK).
Channing: A Replica, a superior Auton used by the Nestene in its attempt to take control of Earth (AAA).