Adric

Adric was a companion to the Doctor in his fourth and fifth incarnations.

Biography
Adric was born and lived on the planet Alzarius. He was ranked as an elite and awarded a gold star as a badge for mathematical excellence because he could do large sums in his head. His brother Varsh was a member of a gang of teenage thieves; Adric wanted to join them but was denied. Varsh asked him the embarkation question "Where will you be when the starliner leaves Alzarius?" to which he replied he would be somewhere else entirely. This became tru as he was onboard the TARDIS when it took off. To prove himself to the group he attempted to steal river fruit but failed. (DW: Full Circle).

Adric stowed himself aboard the TARDIS, as the Doctor and Romana would discover later. Cunningly, he pretended to share the agenda of the Three Who Rule, a trio of vampires who lorded over a small community. He then attempted to save Romana from being sacrificed but failed. Both were saved by the Doctor.(DW: State of Decay)

After Romana left (DW: Warriors' Gate) he acted briefly as apprentice to the sage-like Doctor (DW: The Keeper of Traken, Logopolis). This would change, though Tegan and Nyssa joined the Doctor and Adric and when the Doctor regenerated. (DW: Logopolis, Castrovalva)

Often frustrated by his clumsiness, and fiercely competitive, Adric struggled to find a useful role with the others.

Adric had made the decision to attempt a return to E-Space, when, caught up by events, he gave up his life by remaining on board Captain Briggs' freighter, which, traveling through time, crashed into prehistoric Earth and caused the extinction of the dinosaurs. (DW: Earthshock)

Adric's death continued to haunt the Doctor for many years, as seen when his tenth incarnation watched Adric die again -- this time a manifestation of the TARDIS Matrix. (IDW: The Forgotten)

In an alternate version of these events, following interference by the Doctor during an attempt to recover his TARDIS, his sub-consciousness assisted Adric in breaking the final logic code on the Cybermen's computer, allowing Adric to crash land (though survivable) on Earth. Adric survived for 500 years, creating a City of Excellence and ruling over a sentient race of Scorpions that evolved rather than the dinosaurs. The world they and Adric inhabited was created by Adric from Block Transfer Computations. Adric (after 500 years) met up with the fifth incarnation of the Doctor and Nyssa, and accompanied them back to the Victorian era. Adric finally died after assisting the Doctor to recover his TARDIS from Thomas Brewster. (BFA: The Boy That Time Forgot)

Personality and skills
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. (DW: Full Circle)