He acted like a madman.

Genius is but one remove from madness.

Genius is only one remove from insanity.

The prisoners fought one another like so many mad people.

Zen's latest mission is to save the Earth from ecological destruction at the hands of a plant-destroying madman.

The megalomaniac differs from the narcissist by the fact that he wishes to be powerful rather than charming, and seeks to be feared rather than loved. To this type belong many lunatics and most of the great men of history.