The Megara were microcellular metallic biomachines. They could fly through the air. They communicated with each other using a special language. The Megara believed that "humanoids" were inferior because they were not totally capable of knowing the truth.
At one point, a galactic federation appointed them to uphold the law. The Megara found the federation in contempt of court and destroyed the galaxy. They were sometimes assigned to transport prisoners. When two of them transported Cessair and her servants, she escaped and they pursued her to Earth. (TV: The Stones of Blood)