The Ergon

The Ergon, referred to by the Fifth Doctor as "an" Ergon, was a creature created by Omega as one of his agents in the universe of matter to act on his behalf.

Biography
A reptilian-like creature, (PROSE: Arc of Infinity) the Ergon was one of Omega's less successful attempts at psychosynthesis. (TV: Arc of Infinity) Ace saw it while working at a fast food restaurant and mistook it for a person wearing a costume. (PROSE: Anti-Matter with Fries)

It used a matter converter, with which it shot Colin Frazer, Tegan Jovanka and Robin Stuart. While the Fifth Doctor wrestled with the Ergon, Nyssa took its gun and shot it. (TV: Arc of Infinity)

Tegan later described the Ergon as "looking suspiciously like a plucked chicken". (AUDIO: The Waters of Amsterdam)