Donald Trump's special advisor on regulation, Carl Icahn, told CNBC that he believes the president-elect can stop what he considers to be foolishness in regulation in the United States.

Icahn, a frequent critic of some Obama administration rules, told CNBC's "Fast Money" on Monday that before Trump's victory, he thought "this country was going downhill fast," adding that he still thinks there are problems.

"I really backed Donald. Number one, I think he's smart and I think he's one of the few people that can really shake up the establishment and stop what I consider to be almost idiocy with this overregulation," Icahn said.

The billionaire investor said, however, that there is good regulation and that he supports regulation of Wall Street. But generally, regulations have "run amok," he said.

Icahn, a major fossil fuel investor, has frequently criticized Obama administration energy restrictions. He previously told CNBC that he supported Trump's choice of Oklahoma Attorney General Scott Pruitt, who has battled the current president's EPA and expressed doubts about how much humans affect climate change. Icahn previously said the EPA was one of the worst-run agencies he had ever seen.

Icahn argued that by cutting back on regulations, businesses will no longer feel that "they are at war with the government." He said that change in sentiment will be a "great thing for our economy and it will create jobs because it will create investment."

— CNBC's Jacob Pramuk contributed to this report.