Megara

The Megara are a sapient species of living "bio-machines". They describe themselves as "justice machines" and operate both as an interstellar police force and justice system, sworn to uphold law, arrest criminals, trial them and carry out the sentences themselves.

Biology
The Megara physically resemble floating dots of light which change their apparent size as they speak. Each individual is composed of a small collection of such dots. Despite acknowledging themselves as machines, their bodies are actually made of living cells, described as microcellular metallic organisms or "bio-machines".

Culture and society
The Megara are a proud species which dedicate themselves to upholding the law, arresting and judging criminals. They openly describe themselves as "judge, jury and executioner". Although they pride themselves in their impartiality, they consider their law the only kind of law there is, and have demonstrated contempt for humanoids, which they consider inferior creatures incapable of comprehending the subtleties of law.

Their technology includes means to detect lies as well as to probe the minds of other creatures in search of information. However, they have a strict code against using this method except in cases where the subject is unconscious or otherwise incapable of being questioned by more traditional means.

Appearances

 * Doctor Who, season 16, "The Stones of Blood" (1978)