Learn English – adjective from business

Magnate: a person of great influence, importance, or standing in a particular enterprise, field of business, etc. I don't think there's any special word for deceased magnates (though they often are).

There's also tycoon, but for me at least this suggests someone who is outstandingly successful at making money out of an industry, rather than revolutionalising how that industry functions.

Mogul is much associated with the movie industry of the mid-20th century. Again I feel this suggests someone who wields great power and wealth obtained primarily by business acumen, rather than creativity within the business. I don't normally think of of great movie directors as moguls, for example.

When you don't know how to use your firearm, you become a menace.

As used here, menace is a noun meaning:

A person or thing that is likely to cause harm; a threat or danger