Scandal-hit Scott Pruitt has resigned as head of the US Environmental Protection Agency.
US President Donald Trump said Mr Pruitt had done "an outstanding job, and I will always be thankful to him".
I have accepted the resignation of Scott Pruitt as the Administrator of the Environmental Protection Agency. Within the Agency Scott has done an outstanding job, and I will always be thankful to him for this. The Senate confirmed Deputy at EPA, Andrew Wheeler, will...— Donald J. Trump (@realDonaldTrump) July 5, 2018
But Mr Pruitt has been embroiled in allegations of ethics violations for months, including issues with his travel and security expenses and a condo arrangement.
His deputy Andrew Wheeler will take over as acting head of the agency, Mr Trump said.
Mr Pruitt is the subject of at least a dozen investigations into his conduct.
He has been under scrutiny for renting an apartment with ties to a fossil fuels lobbyist.
He is also accused of bypassing the White House to secure big pay rises for two long-time staff members.
Some of the ethics accusations involved jobs for Pruitt's wife. Emails obtained by the Sierra Club environmental group showed Mr Pruitt had an aide contact the chief executive of a fast-food chain about his wife becoming a franchise owner. The Washington Post reported Pruitt had aides try to get her a job at the Republican Attorneys General Association with a salary topping $US200,000.
During congressional testimony in April, Mr Pruitt was unapologetic, often blaming his staff for any agency missteps. Lawmakers posed tough questions on a range of issues also including raises for top aides and reports of retaliation against EPA whistleblowers. Democrats accused him of endless misconduct.
Mr Pruitt, a close ally of the fossil fuel industry, also was known for questioning the human role in global climate change. As Oklahoma's former attorney general, he waged a legal fight against the environmental rules implemented by the agency he eventually would head.
From a policy perspective, Mr Pruitt was one of Mr Trump's most effective cabinet members.
Mr Trump has praised Mr Pruitt for slashing regulations on the energy and manufacturing industries, including his move to repeal Democratic former president Barack Obama's signature program to cut carbon emissions from power plants, known as the Clean Power Plan.
Mr Pruitt also was instrumental last year in lobbying Mr Trump to withdraw the US from the global 2015 Paris climate accord to combat global warming.
Democratic US Representative Gerry Connolly said after his resignation: "Scott Pruitt's reign of venality is finally over. He made swamp creatures blush with his shameless excesses. All tolerated because Trump liked his zealotry. Shame."
- BBC / Reuters