Adric (Matthew Waterhouse)
Adric, a teenage boy with a gift - and badge - for mathematical excellence, was a member of a street gang on the planet Alzarius, along with his brother, Varsh. Adric, alone and hungry for adventure, stowed away in the TARDIS after Varsh sacrificed his life to save the Doctor and his friends.
Often frustrated by his clumsiness, and fiercely competitive, Adric struggled to find a useful role among the TARDIS crew. He ultimately gave up his life by remaining on board a spaceship that crashed into prehistoric Earth, causing the death of the dinosaurs.