Professor Lloyd Cycloid is a minor villain in the 1987 TV series episode, "Donatello Makes Time". He is an evil mad scientist who was traveling in the sewer, when he spotted Donatello's latest invention, the Time Stopper. After making off with it, he used the invention to also steal the iridium head of the pharaoh Tu-Tu Karmen and a laser gun that April O'Neil was reporting on for Channel 6.
Donatello tracked him down, only to fall victim to his own invention. Professor Cycloid froze Donatello in time, tied him upside-down and suspended him over a vat of acid. Furthermore, he had Donatello attached to a door handle, so that when anyone opened the door, he would be dropped in the acid.
Cycloid's ultimate goal was to create a satellite that would make everyone else on the planet stupid; his goal with the iridium and the laser was to craft a helmet that would protect him from the satellite's effects. However, Donatello successfully thwarted that attempt, and after saving Donatello, the other three Turtles apprehended Cycloid. After his defeat, he is left to the police and presumably sent to prison.