Adric is a fictional character played by Matthew Waterhouse in the long-running British science fiction television series Doctor Who. He was a young native of the planet Alzarius, which exists in the parallel universe of E-Space. A companion of the Fourth and Fifth Doctors, he was a regular in the programme from 1980 to 1982. The name Adric is an anagram derived from Nobel Prize-winning physicist Paul Dirac. Waterhouse was the youngest male actor to play a companion.

Adric first appeared in the Fourth Doctor serial, Full Circle . Attempting to escape from the mysterious Mistfall that was threatening his community, he stumbled across and found refuge in the TARDIS, which had been drawn into E-Space via a wormhole-like phenomenon known as a Charged Vacuum Emboitment. He stowed away when the Doctor and Romana left Alzarius and accompanied them on the rest of their adventures in E-Space, remaining with the Doctor when Romana left, and the TARDIS eventually managed to find its way back into its own universe.

With a brilliant mathematical mind and sporting a gold badge for mathematical excellence, Adric was also very well aware of his own intelligence. That, coupled with his relative immaturity, led to a personality that was abrasive and crossed over into arrogance. As a result, Adric is one of the least popular companions among fans of the programme. However, it was obvious that Adric also desperately sought validation from the Doctor as well as those around him, and was often hurt and resentful if he felt he was being sidelined or unable to contribute.

Adric was present when, during the events of Logopolis, the Fourth Doctor fell from the Pharos Project radio telescope and regenerated into his fifth incarnation. He continued to travel in the TARDIS along with new companions Nyssa and Tegan, but his travels came to an end in Earthshock when he tried to stop a Cyberman-controlled freighter from crashing into prehistoric Earth. The navigational controls had been locked by logic codes, and Adric was entering the solution to the last code when the computer was destroyed by a dying Cyberman. Unable to even tell if he had been right, he died in the crash while his fellow crewmates watched it in horror on the TARDIS viewscreen. Adric died not knowing that the freighter he was trying to stop was actually destined to be the "meteor" that would wipe out the dinosaurs.

Adric's death affected the Doctor deeply and continues to haunt him more the death of any other companion, except for perhaps Katarina.

Matthew Waterhouse returned as a hallucinatory image of Adric in Time-Flight and also as part of the regeneration sequence in The Caves of Androzani. A ghost of Adric features in the plot of David Bishop 's spin-off novel Empire of Death.

• Travelled from: Full Circle to Earthshock