Adric was a companion to the Fourth and Fifth Doctors. He grew up in another universe called E-Space and died trying to stop Captain Briggs' freighter from crashing into Earth.
Adric stowed away on the TARDIS and was discovered by the Fourth Doctor and Romana. He pretended to share the agenda of the Three Who Rule, a trio of vampires who ruled over a small community. He tried to save Romana from being sacrificed but failed; both were saved by the Doctor. Adric's relationship with the Doctor deteriorated after the Fourth Doctor regenerated and Tegan and Nyssa began travelling in the TARDIS. Adric believed the girls were a hindrance to his relationship with the Doctor. He also had a clear preference for the Fourth Doctor.
Adric was often fiercely competitive, yet frustrated by his clumsiness. He whined a lot, and struggled to find a useful role in the TARDIS crew. He finally told the Doctor he wanted to return to E-Space. After showing the Doctor his computations to engineer the return, Adric admitted he really wished to remain on the TARDIS. He was caught up in a failed plan of the Cybermen to bombard the Earth with with Briggs' freighter. He died by remaining on board the crashing, time-travelling ship. With Adric onboard, it crashed into prehistoric Earth, causing the extinction of the dinosaurs.
Adric was a mathematical genius, and let everyone know it. He was very proud of his Elite status. He wished to be accepted by his brother Varsh's gang, the Outlers, and tried to steal fruit to prove himself, but failed. When his brother died, he kept his belt, a symbol of Outler membership. He pretended to go along with the plans of the vampires in a ploy to rescue Romana, with whom he got on well. In a misguided bit of overconfidence, he died by remaining on board Captain Briggs's freighter to try and prevent it from crashing into the Earth. He died holding his brother's belt.
Adric was fiercely loyal to the Doctor and had a generally amicable relationship with the Time Lord, who resigned himself to act as his mentor. Adric could be annoying at times, but wanted desperately to be brave and accepted; he defied the Master and died trying to solve a math/computer problem. As he crashed to his death, unable to access the computer system to input his last mathematical calculation, he said, "Now I'll never know if I was right."