Walter Shaub, director of the Office of Government Ethics (OGE), has announced his resignation after repeatedly clashing with President Donald Trump.
The OGE is the US government's top independent watchdog that helps officials avoid conflict of interest.
Its role is more important now, given Trump's sprawling business empire and the wealthy people he has appointed to his cabinet.
US government's ethics chief resigns
Trump conflict of interest: A primer
The Donald Trump presidency has been subject to intense public scrutiny with respect to the conflicts of interests flowing from the Trump family's involvement in hotel and real estate businesses.
Appointments, including those made to the Department of Justice and the National Labor Relations Board, drew criticism from political commentators.
Ethics experts say these conflicts of interest give room for bias and are unconstitutional.
Shaub takes parting shot at Trump after resigning
Shaub will leave his post on July 19.
In a parting shot aimed at Trump, Shaub said in a statement: "In working with the current administration, it has become clear to me that we need improvements to the existing ethics program."
The White House said it "appreciates his service" in a statement, adding that Trump would appoint his successor.
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Shaub's clashes with Trump administration
Shaub strongly criticized Trump following his 2016 election win over his failure to divest from his business holdings.
Shaub had said he was "extremely troubled" by Trump's decisions of handing over control of his business empire to his sons. He said the move didn't match "standards" of US presidents over the last 40 years.
Shaub had similar reservations about Trump's wealthy Cabinet nominees.
Shaub had called for investigation into presidential aide Kellyanne Conway
In February, Shaub called for a White House investigation into presidential aide Kellyanne Conway over her controversial suggestion that Americans should buy the president's daughter Ivanka Trump's products. Despite the repeated disagreements, Shaub said Trump never pressurized him to stand down.
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