madman
n.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.”
Often used in the simile 'like a madman' to describe intense or reckless activity.
From mad + -man.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.