Homeless Man in YouTube $100 Challenge Dead -- Dies From Alcoholism

The $100 homeless man who became famous for his generosity has died ... TMZ has learned.

We're told Kenni Thomas Nickel -- featured in a YouTube video that generated 40 million views -- was found dead in an L.A. alleyway. The L.A. County Coroner's Office tells us Nickel died from chronic alcohol abuse. He passed away last month.

You'll recall, a stranger gave Nickel $100 and then followed him around with a hidden camera to see how Nickel spent it. To everyone's surprise, Nickel used the cash to dish out food and other necessities to homeless people.

Nickel was 56.

R.I.P.