While Mark Cuban now has a net worth of $4.1 billion, he was once so strapped he didn't even have enough money to get a bank account.

The revelation came on Sunday's episode of "Shark Tank," during a pitch for fintech start-up Spare, a virtual ATM network that is aimed at users who don't have access to financial resources and are therefore "under-banked."

"When I was broke and sleeping on the couch, I couldn't open up a bank account. You needed to have 200 bucks. You needed this, you needed that. They didn't give me one," said Cuban (who ended up investing $500,000 in Spare).

It's hard to imagine Cuban that broke, but the tech billionaire and Dallas Mavericks owner came from humble beginnings. He was born and raised by a working class family in Pittsburgh, Pennsylvania. As a teenager, he reportedly resold baseball cards, stamps and coins to make money.

"People thought I might go work at a mill. My mom wanted me to learn how to lay carpet because she was concerned about my future," Cuban said in a previous episode of "Shark Tank."

Then, after graduating Indiana University in Bloomington, a 24-year-old Cuban moved to Dallas with $60 to his name. He shared a $600-a-month three-bedroom apartment with five other guys. He says he slept on either the floor or couch and didn't have a closet. He worked as a bartender at a club to make ends meet.

He also tried other gigs: "I had quit or been fired from three straight jobs," said Cuban on a previous episode of "Shark Tank."

But eventually, Cuban got into computers.

"When I got one of my first jobs out of school using technology, it was like, wait, I love this. I've taught myself the program, I could go seven hours, eight hours without taking a break thinking it was 10 minutes because I was concentrating so hard and so excited and really loved it. And that's when I realized that I can be really, really good at technology."

So Cuban started his own business, MicroSolutions, which he sold to CompuServe for $6 million in 1990.

Five years later, Cuban and his friend Todd Wagner created an online streaming audio service called Broadcast.com so they could listen to Hoosiers games from Texas. Yahoo acquired the business in 1999 for $5.7 billion in stock.

"Nobody had high hopes for me," Cuban said. "But I was a hustler."

Disclosure: CNBC owns the exclusive off-network cable rights to ABC's "Shark Tank."

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