The Event Synthesizer was an immense biomechanical device created by the Lords of Althrace to regulate the flow of time. Its controls, which resembled an organ's keyboard, were operated by the Prime Mover, who used the Synthesiser to help keep the universe running harmoniously.
In the early 1980s, the Prime Mover accidentally struck a wrong note for the first time in centuries, disrupting the harmony and creating gaps in time. Melanicus escaped his imprisonment through one of these and seized control of the Event Synthesizer. He removed the device from time to prevent attack and used it to create death and chaos throughout time, including the Millennium Wars. He was defeated by the Fifth Doctor, Sir Justin, and Shayde, and control of the Event Synthesizer was restored to the Prime Mover. (COMIC: The Tides of Time)