A lawyer who spent much of his career protecting banks is now in charge of regulating them.

And last week’s appointment of the lawyer, Keith A. Noreika, to run the Office of the Comptroller of the Currency is unusual because it does not require him to sign the ethics pledge that President Trump is forcing on other appointees.

Mr. Noreika, who is signaling plans to unwind some Obama-era banking regulations, got the job after the Trump administration removed Thomas J. Curry, an Obama appointee, as the comptroller. Mr. Curry’s term expired in April. On Thursday, Mr. Noreika told employees that Mr. Curry’s chief of staff was also leaving the agency, according to an internal email and two people briefed on the matter.

The chief of staff, a Democrat and a supporter of bank regulation, announced plans to step down after Mr. Noreika indicated that he wanted to hire his own top adviser, one of the people said.

Unlike Mr. Curry, a longtime regulator, Mr. Noreika joined the agency from the prominent law firm Simpson Thacher & Bartlett, where he represented an array of banks. Many of his former clients are regulated by the Office of the Comptroller of the Currency, including at least one bank that may need the agency’s blessing for a merger, a matter on which Mr. Noreika worked.