How these 3 janitors went on to become self-made millionaires

With hard work, perseverance and luck, three men who started as janitors became self-made millionaires.

Each of the men approached their success differently, but each, in his own way, did what it takes to succeed and amass wealth through savvy investing, seeking out opportunities and making every day count. Here are there inspiring stories.

1. Sean Conlon

An immigrant from Ireland, Sean Conlon arrived in Chicago with $500 and started out as an assistant janitor .

Back home, his family hadn't had much. Once, a bank had even tried to repossess his family house, which may have inspired Conlon to become a real estate mogul (and the star of CNBC's " The Deed: Chicago ").

Conlon worked hard to save money, which he eventually used to buy his first apartment. He began selling real estate at night, and ultimately became one of the top real estate brokers in the country.

And he credits much of his success to the possibilities in the United States. "I understood fairly quickly that real estate is a tangible path to wealth," says Conlon. "I was an ordinary person who did some fairly extraordinary things. It's America. You can still do those things."

2. Ronald Read

Once a janitor and gas station attendant, Vermont's Ronald Read quietly became a self-made millionaire without a hefty annual salary.

Read, who passed away at age 92 in June 2014, put together an $8 million portfolio, one even his family didn't know about until his death.

He reportedly had at least 95 stocks when he passed away and was said to live a frugal lifestyle. Read gave most of his wealth to the hospital and library in Brattleboro, Vermont, where he lived his entire life.

3. Steve Hightower

Originally from Ohio, Hightower worked nights and weekends for his family's cleaning business. He continued working as a custodian in college as well.

Now Hightower has his own oil and transport business, which he started in 1981. In 2017, the company aims to make $500 million.

"I started as a janitor. I started cleaning floors and toilets and doing those things that most people would never even dream of doing," says Hightower. However, he adds, "I wanted more."

"When people ask me would I ever have imagined I would be where I am today? Absolutely," Hightower tells CNBC. "Because if you don't think that you can be great, you'll never be great. And I knew that I was gonna be great a long, long time ago."

The oil tycoon explains that his experience starting from humble beginnings has had a huge impact on his life today. "I still haven't made it. I'm still a very humble individual who's trying to do the best that they can and one day actually make it," says Hightower. "Because I understand what real money is."