A is for... Adric

Travelling companion to the Fourth and Fifth Doctors. Adric was born in the pocket universe of E-Space, on the planet Alzarius - one of the colony of stranded Terradonians whose Starliner had crashed there. Adric's parents died when he was a child, and he only had his older brother Varsh for family. He was a precocious youth, gaining a badge for mathematical excellence from the community. Varsh and some friends rebelled against the Starliner society, and set themselves up as Outlers, living in a cave on a hillside overlooking their old home. Adric was desperate to join them. When the Outlers failed to steal enough river fruits Adric chose to prove himself by obtaining more. This coincided with a period called Mistfall, which the Terradonians feared. The air would turn toxic, so everyone retreated into the Starliner which was then sealed up. Adric witnessed the death of one of the Deciders who ruled their society. Decider Draith was puled into the lake as the mists rose. The boy then stumbled into the TARDIS, where he met the Doctor, Romana and K9. They were surprised when an injury to his knee healed in only an hour or so.
The Doctor later discovered that Adric's people were not from Terradon at all, but were the product of Alzarius' bizarre evolutionary processes. Adric proved to be light-fingered, stealing an image converter for the Doctor, as his own one did not work in E-Space. He allowed his brother and the other Outlers to attempt to steal the TARDIS, and then abandoned Romana in the cave when she was attacked by giant spiders. Later, he saw his brother killed at the hands of the Marshmen.
When the Doctor and Romana left Alzarius, they did not realise that Adric had stowed away on board. When he emerged from hiding, he tricked K9 into letting him go. On the planet ruled by Vampires, Adric was selected to become one of the Chosen Ones - a servant to the Great Vampire which was about to be resurrected. Adric seemed to ally himself against the Doctor and Romana, but later claimed that this was a ruse.

When the TARDIS left E-Space, leaving Romana and K9 behind, Adric continued to travel with the Doctor in Normal Space. He attempted to study the Doctor's diaries, and rapidly learned a great deal from the ship's data banks. On Traken he first met the future companion Nyssa, with whom he formed a bond. Together they tried to destroy the Melkur when it took control over the planet's controlling force - the Source. It was Adric who identified that the Melkur was really a disguised TARDIS. Adric was looking forward to a visit to the Doctor's homeworld when the Doctor changed his plans and decided to fix the TARDIS chameleon circuit instead. This involved a trip to present day England, where Australian Air Hostess Tegan Jovanka blundered aboard, and then a visit to the planet of Logopolis, where Adric was pleased to be reunited with Nyssa. Adric helped the Logopolitan Monitor to save the Doctor when the Master interfered with the Block Transfer Computations - resulting in the ship shrinking. The mysterious Watcher took Adric and Nyssa outside of the Universe when the Master's tamperings began to spread an entropy field.
Adric was present when the Doctor fell from a radio telescope at the Pharos Project on Earth, causing him to regenerate into his Fifth incarnation.
The Master then kidnapped Adric and used his mathematical skills to try to destroy the TARDIS in the Big Bang, and later he was employed to create a whole fake township on Castrovalva, which proved to be an elaborate trap.
Whilst he got on well with Nyssa, Adric did not take to Tegan, and the dynamic in the TARDIS with a new Doctor led to Adric feeling side-lined. He also made a few errors of judgement - allying himself with people who opposed the Doctor.
On the planet Deva Loka, Adric panicked and ran off in an armoured exploration vehicle - inadvertently stopping the Mara-possessed Aris from carrying out an attack on the human colonists' base. Adric's ability to pretend to ally himself with Hindle allowed him to remain at large and try to help free the Doctor and scientist Todd.
Soon, Adric announced that he wanted to travel back home into E-Space, to find the Starliner people. The Doctor was furious with him, as the journey would be extremely hazardous. He would later say that he was not really serious about this - just wanting to prove to the Doctor that the trip was possible. The TARDIS crew then became caught up in a Cyberman plot to wipe out a conference on 26th Century Earth. Adric was left aboard a bomb-laden freighter that was on a collision course with the planet, its systems over-ridden by a Cyberman logic device. Adric attempted to unlock this - causing the freighter to hurtle back in time some 65 million years. Its collision would be the cause of the destruction of the dinosaurs - and hence the rise of humankind.
Adric was able to escape but elected not to, so that he could finish his work. A dying Cyberman prevented him from succeeding, and he perished in the crash. In his final moments, he clutched his brother's belt for comfort. The Doctor used Adric's gold-rimmed star badge to destroy the Cyber-Leader.
Soon after, the Master, harnessing the power of the Xeraphin, used an image of Adric to try to get Nyssa and Tegan to turn back from entering his domain in prehistoric Earth.
The Fifth Doctor felt guilt at the boy's death until the end of his incarnation. Adric's name was the last word he uttered.

Played by Matthew Waterhouse. Appearances: Full Circle (1980) to Earthshock (1982). Cameos in Time-Flight (1982) and The Caves of Androzani (1984).

• An interesting concept for a companion whose potential was squandered by subsequent writers. Waterhouse was not the most experienced actor, but a lot of the bad reputation both actor and character had suffered over the years is not always deserved.
• The character has been resurrected on audio, played by Waterhouse, for stories set between Castrovalva and Earthshock. The Big Finish version of Nyssa has her name her son after him. Matthew now lives in the US and is a writer.