Donald Trump called Carl Icahn "one of the world’s great businessmen" in a statement Wednesday. | Getty Trump taps investor Icahn to advise on regulatory reform

Carl Icahn has been picked by President-elect Donald Trump to be a special adviser for overhauling regulations, putting the billionaire investor in a position to shape rules affecting businesses in which he has stakes.

“Carl was with me from the beginning and with his being one of the world’s great businessmen, that was something I truly appreciated," Trump said in a statement. “His help on the strangling regulations that our country is faced with will be invaluable.”

Icahn — whose net worth is $21.6 billion, according to Forbes — endorsed Trump, who repeatedly mentioned him as a potential Treasury secretary, lead negotiator on trade deals with China and Japan, or both.

Both men have spoken of the need for regulatory reform as key to jumpstarting the economy.

“It’s time to break free of excessive regulation,” Icahn said in the statement Trump’s transition team released.

Icahn, 80, is chairman of Icahn Enterprises, which is based in New York and has about 65,000 employees. Its investments have ranged from Hertz, a rental car company, to Herbalife, a personal-care provider. It has also had stakes in industries including railroads, casinos and hotels, tires and oil.

He will be advising Trump in an individual capacity and will not be serving as a federal employee or a special government employee and will not have specific duties, the transition team said.

Democrats quickly criticized Trump’s pick of Icahn, focusing on conflicts-of-interest concerns and the past business deals between the two New Yorkers.

“Icahn has billions in stock holdings … he will also be in charge of overseeing regulatory overhauls while simultaneously controlling or owning stock in companies that could benefit from the changes he makes,” said Eric Walker, the communications director for the Democratic National Committee. “It looks like Trump isn’t the only billionaire set to profit off of the presidency.”

Walker added, “This is a quid-pro-quo 25 years in the making. In the early 1990s, Icahn came to Trump’s rescue as his casino business was failing.”

Icahn has already wielded considerable influence in the Trump transition. He played a central role in vetting the president-elect’s list of picks to lead the EPA. Scott Pruitt, the attorney general of Oklahoma, was eventually selected.

Icahn came to believe that Pruitt is open to changing an obscure part of EPA's ethanol rule that the oil refinery-owning investor had been railing against for months, POLITICO reported.

Yet Icahn has favored some regulations when they benefit his investment model. As an activist shareholder, his firm buys stakes in companies he sees as underperforming and in need of a shakeup.

Thus, he has supported regulations that make it easier for shareholders to vote on boardroom decisions. When the SEC in October proposed rules to expand voting options with universal proxy ballots for shareholders, Icahn applauded.

“This change will be extremely positive for our capital markets and [I] am hopeful that the powerful voices in opposition to the universal proxy card, such as the U.S. Chamber of Commerce, will not be successful in defeating this important initiative, as they were when the SEC attempted to introduce proxy access,” Icahn said in an Oct. 27 statement.

Notably, the SEC’s Democratic commissioner voted for the proposal while the agency’s Republican member did not.

As a presidential candidate, Trump attacked the Chamber for its support of the Trans-Pacific Partnership trade deal. A spokeswoman for the Chamber said the group declines to comment on appointments.

“Libertarian Republicans agree with Icahn that private funds can add value,” said J.W. Verret, associate professor of law at George Mason University's Antonin Scalia Law School. “Establishment Republicans don’t always agree.”