Adric first appears in the Fourth Doctor serial, Full Circle. Attempting to escape from the mysterious Mistfall threatening his community, he stumbles across and finds refuge in the TARDIS, which has been drawn into E-Space via a wormhole-like phenomenon known as a Charged Vacuum Emboitment. He stowed away when the Doctor and Romana and K-9 Mark II left Alzarius and becomes a companion in the following serial, State of Decay, accompanying them on the rest of their adventures in E-Space. He remains with the Doctor when Romana and K-9 Mark II leave and the TARDIS finds its way back into its own universe.
With a brilliant mathematical mind and sporting a star-shaped badge (blue enamel with gold backing) for mathematical excellence, Adric is also very well aware of his own intelligence. This, coupled with his relative immaturity, leads to a personality that is abrasive and occasionally crosses over into arrogance. As a result, Adric is one of the least popular companions among fans of the programme. However, it is obvious that Adric also desperately seeks validation from the Doctor as well as those around him, and is often hurt and resentful if he feels he is being sidelined or unable to contribute. As an Alzarian, Adric is a member of a species of extremely adaptable creatures, theoretically capable of genetically evolving to suit any environment, though it is unknown if his particular substrain is capable of this. It is known that he possesses an inhumanly rapid rate of healing, though not to the extent he can regenerate amputated body parts.
Adric is present when, during the events of Logopolis, the Fourth Doctor falls from the Pharos Project radio telescope and regenerates into his fifth incarnation. He continues to travel in the TARDIS along with new companions Nyssa and Tegan, but his travels come to an end in Earthshock when he tries to stop a Cyberman-controlled freighter from crashing into prehistoric Earth. The navigational controls had been locked by logic codes, and Adric is entering the solution to the last code when the computer is destroyed by a dying Cyberman. He dies in the crash, while his fellow crewmates watch in horror on the TARDIS viewscreen. His last words before the explosion kills him are "Now I'll never know if I was right." Adric also dies not knowing that the freighter he was trying to stop was actually destined to be the "meteor" that would wipe out the dinosaurs (see Cretaceous–Tertiary extinction event and Alvarez hypothesis).
Adric's death affects his companions deeply. In Time-Flight, Tegan tries to persuade the Doctor to go back in time and save him, but the Doctor refuses to break the Laws of Time, even though it obviously pains him. The Xeraphin try to use an illusion of Adric pleading that if they travelled any further they would kill him, an effort by Xeraphin to stop Nyssa and Tegan from travelling further in the same story, but they see through the deception when they realise Adric is still wearing his badge (which the Doctor had destroyed in order to kill a Cyberman) and travel forth giving Adric another illusory death scene. Adric also appears as a hallucination at the end of The Caves of Androzani, and his name is the last word that the Fifth Doctor says as he "dies", regenerating into the Sixth Doctor.