The Alzarians are the sapient humanoid inhabitants of the planet Alzarius, which look externally identical to Humans. They lived in and around the remains of a crashed Terradonian star-liner and believed themselves to be descendants of the original crew, which have crashed over four thousand generations ago. They live in fear of the native Marshmen and other native life forms which displayed the ability to rapidly evolve in response to their environment. During the period known as Mistfall, which takes place every fifty years approximately, the Alzarians had to seek protection against the toxic gases released from the swamps.
As it turns out, however, the Alzarians are actually native to the planet, and are an evolutionary mutation of the Marshmen, which several millennia ago attacked the Terradonian crew and evolved into a new form to replaced them, which ended up looking identical to the Terradonians. Whether horizontal gene transference or some kind of Lamarckian evolution was involved in the process is unknown. When examining them under the microscope, the Doctor noticed that the cells of each Alzarian species (Alzarians, Marshmen and Alzarian Spiders) looked exactly identical, and also determined that they have the same DNA. Due to their origins, the Alzarians are actually far more adapted to their environment than they realize, as they share the Marshmen's abilities to breathe the toxic gases released during Mistfall and to heal injuries extremely fast.
The Alzarian government is an oligarchy, lead by a group of Deciders. They modeled their society after the Terradonians, whom they believed were their ancestors; and dedicated their existence to attempting to repair the star-liner with the goal of one day returning to Terradon. They believed that about 40 generations had passed since the day of the crash, but the real number was about a hundred times greater than that. This fact had been hidden from the population, as the Alzarian leaders were aware that they completely lacked the ability to flight the ship, even though it was by this point fully operational. They decided it would be best for their people to live with false hope than to accept the truth of their situation. Eventually, the Alzarians received help from the Fourth Doctor, who explained their real origins and assisted them to fly in the star-liner; not to Terradon, but to a new world that could be colonized by them.
- Doctor Who season 18 - Full Circle (1980) (First appearance)
- Adric subsequently appeared in all episodes until season 19's Earthshock