Jalnik

Jalnik was a 40th century human scientist.

Due to his time experiments, he unleashed the Pantophagen on Earth from their origin in an other dimension. In this alternate timeline, the planet of the fortieth century was nearly annihilated. He went back to 1977 to prepare the way for the survivors to escape.

However, some Pantophagen DNA combined with his and resulted in him becoming a Pantophagen-human hybrid; he was described as having a right side that resembled a grasshopper, and was dependent on regular consumption of fresh meat to maintain some kind of sanity, to the point that he could devour an adult human in seconds. This condition eventually had an effect on his mind, leading to Jalnik making plans to unleash the rest of the Pantophagen on Earth in 1977 while mutating other survivors of his time into more hybrids like himself, convinced that he was talking to the Pantophagen when in fact it was just mutation-induced insanity.

The Fourth Doctor and Leela stopped him and the migration, which could have caused a temporal paradox with universal ramifications, ending with Jalnik being eaten by the true Pantophagen as the circumstances that led to his own future were erased. (AUDIO: The Foe from the Future)