Midas

Professor Midas was a scientist who invented a ray machine that could turn a person's body into plastic, essentially making them immortal and indestructible. A second dose, however, would disintegrate the person, killing them.

The machine also allowed Midas to control the mind of any person he used it on. Intending to use his device to seize power, he treated his own body with the ray, then used it on the inhabitants of Puddlesfield, making them his slaves.

When the cast and crew of The Squire of Crampton started filming on location near his base, he used the device on the TV film, hoping to transfer its transforming qualities to it, causing it to affect whoever watched it. When he accidentally transformed the cast and crew as well, the Ministry of Defence sent the Third Doctor to investigate. He discovered Midas' plans, narrowly avoided being turned into a plastic slave himself, and modified the device to return the villagers back to normal.

When Midas attempted to use his device on a British Army tank that had been made shiny on the Doctor's orders, the ray was reflected back on him, disintegrating him. The Doctor then had the ray machines destroyed. (COMIC: The Celluloid Midas)

Behind the scenes
It is implied that Midas was only a nickname and not the scientist's real name.