He is a 'madman' out on the ski slopes. [=he is an extremely daring or reckless skier]
He drives 'like a madman'. [=he drives very recklessly]
a celebrity being stalked by a 'madman'
(..) And when we faced extinction, I offered a solution. Genocide. But random, dispassionate, fair to rich and poor alike. They called me a madman. And what I predicted came to pass. Congratulations, you're a prophet. I'm a survivor. (..)2018 Avengers: Infinity War