Michael Bloomberg, the former New York City mayor, spoke on the third day of the Democratic National Convention. Joe Raedle/Getty Images Billionaire Michael Bloomberg stung Donald Trump on Wednesday night with a brutal critique in front of the Democratic National Convention in Philadelphia, during which he repeatedly skewered the Republican presidential nominee's business practices.

The former New York City mayor, ranked by Forbes as the eighth-richest man in the world, began his address by acknowledging that he was an "outsider" who would be delivering an "unconventional convention speech."

"I've been a Democrat. I've been a Republican. And I eventually became an independent because I don't believe either party has a monopoly on good ideas or good leadership," he said at the start of his speech, earning some boos shortly after for offering minor critiques of Democrats.

Bloomberg quickly, however, focused his attention on Trump, whom he called a "dangerous demagogue."

Bloomberg: We must unite around Clinton "who can defeat a dangerous demagogue" #DemsInPhilly https://t.co/TAG0SqRvbP https://t.co/fzaaT4JInp — CNN Politics (@CNNPolitics) July 28, 2016

"I built a business, and I didn't start it with a million-dollar check from my father," the billionaire said, referring to the money Trump's father loaned him to start his first business.

Bloomberg, who like Trump is a New York businessman and who almost threw his hat in the ring for the presidency in 2016, slammed Trump's business practices and argued that they would be dangerous to the US economy.

"Trump says he wants to run our nation like he runs his business? God help us," Bloomberg said to thunderous agreement from the crowd. "I'm a New Yorker, and I know a con when I see one."

He added: "The richest thing about Donald Trump is his hypocrisy."

Bloomberg said he understood the "appeal of a businessman" as president, but he contended that Trump would "make it harder for small businesses to compete" and would "do damage to our economy."

"Trump is a risky, reckless, and radical choice, and we can't afford to make that choice," he said.

Bloomberg didn't quite offer Clinton a ringing endorsement, acknowledging that he disagreed with her on numerous issues, but he said she was the "responsible choice in this election" and a "sane," "competent" candidate.

"Hillary Clinton understands this isn't reality television — this is reality," he said. "She understands the job of president. It involves finding solutions, not pointing fingers."