HAVING HELD partial or controlling stakes in companies ranging from Phillips Petroleum to American Railcar Industries, billionaire investor Carl Icahn certainly knows a thing or two about how federal regulators deal with business. He also is, at 80, a successful, intelligent, deeply experienced investment pro. Whether his is the ideal résumé for a special adviser to the president on regulatory reform is less clear. Foxes are experts on chicken coops, it is true.

Federal safety, environmental and financial regulations necessarily involve balancing of costs and benefits to the public. The Obama administration’s approach frequently struck the balance in favor of more rules, and there is a reasonable case to be made that pruning regulatory overgrowth could, indeed, help the economy — which, by the way, is doing reasonably well. But Mr. Icahn’s sweeping indictments of the regulatory agencies, voiced repeatedly during the campaign, suggest he would urge President-elect Donald Trump to swing wildly in the opposite direction. “You almost get enraged by some of the stuff,” he told CNBC on Thursday.

The Trump transition team’s statement announcing Mr. Icahn’s new role quoted him as saying that “under President Obama, America’s business owners have been crippled by over $1 trillion in new regulations.” We don’t know where that number comes from, though we did find an estimate from the conservative regulation skeptics at American Action Forum, a think tank, that puts the total cost of major new regulation imposed since the beginning of the second term of George W. Bush’s presidency at $1 trillion. Notably, that study also mentioned $745 billion worth of offsetting social benefits.

No doubt Mr. Icahn speaks from genuine principle. But if someone were to charge him with talking his own book, it would be a hard accusation to refute, because his many companies are so frequently and conflictually embroiled with regulators. Mr. Icahn helped vet Mr. Trump’s nominee to head the Environmental Protection Agency, Scott Pruitt, even though Mr. Icahn controls an EPA-regulated oil refiner, CVR Energy, according to the Wall Street Journal. Mr. Icahn’s American Railcar Industries is suing the Federal Railroad Administration for allegedly unlawfully requiring it to test tank cars for leaks.

How, exactly, are Mr. Icahn and, more importantly, Mr. Trump to be held accountable for the inherent conflicts in this situation? The transition team said Mr. Icahn “will be advising the President in his individual capacity and will not be serving as a federal employee or a Special Government Employee and will not have any specific duties.” Nor will he get a salary. Mr. Icahn told CNBC there is no problem because he will not be making policy, just “basically talking to Donald as I’ve talked before.” If anything, this proposed status only compounds the problematic lack of an institutional check on what Mr. Icahn does when “Donald” is president, with the power to move markets.

Mr. Trump praised Mr. Icahn, extravagantly, “as someone who is innately able to predict the future especially having to do with finances and economies.” Perhaps. Neither man, however, seems able to foresee the quite obvious ethical problems they may be creating for the next administration — and themselves.