madman
n. countablen. someone who behaves in a very dangerous, wild, or foolish way. It is often used to describe someone who takes unnecessary risks or acts without thinking.
n. a person who behaves in an extremely foolish, reckless, or irrational manner. While historically used to describe someone with a mental illness, modern usage typically focuses on dangerous or unpredictable behavior.
He drove like a madman through the narrow streets.
The neighbors thought he was a madman for trying to build a three-story boat in his tiny backyard.
History often remembers the visionary as a madman until their seemingly impossible theories are finally proven correct by the passage of time.
From mad + -man.
Often used in the simile 'like a madman' to describe intense or reckless activity.