mad scientist

Short definition from Wiktionary

Noun

1. 1
   A bumbling or eccentric scientist working on questionable projects, or a villainous scientist bent on destruction; sometimes, a complex character in whom these archetypes seem to vie for supremacy: A stock character in fiction who embodies such an archetype.
2. 2
   A bumbling or eccentric scientist working on questionable projects, or a villainous scientist bent on destruction; sometimes, a complex character in whom these archetypes seem to vie for supremacy: A real-life scientist who is asserted to embody such an archetype.
3. 3
   A bumbling or eccentric scientist working on questionable projects, or a villainous scientist bent on destruction; sometimes, a complex character in whom these archetypes seem to vie for supremacy: Used other than figuratively or idiomatically: a scientist who is insane, power-mad, or similarly deranged.