Scott Pruitt's controversial reign as head of the US Environmental Protection Agency has come to an end, with the latest scandal involving allegations he attempted to hide meetings with Australia's Cardinal George Pell at the Vatican.
The New York Times and CNN, quoting former EPA staff, reported on Thursday Mr Pruitt's aides retroactively deleted meetings from his public schedule in what could be potential violations of the US Federal Records Act.
US President Donald Trump has been under pressure for months to fire Mr Pruitt, who has aggressively eradicated environmental protections while facing a constant wave of scandals and potential ethics violations.
"Within the Agency Scott has done an outstanding job, and I will always be thankful to him for this," Mr Trump, announcing Mr Pruitt's resignation in a tweet on Thursday, wrote.
Mr Pruitt's former deputy chief of staff for operations Kevin Chmielewski told CNN EPA staffers routinely met in Mr Pruitt's office to "scrub," alter or remove records from his official calendar.
Mr Pruitt's meetings and a dinner with Cardinal Pell in Italy in June last year did not appear on Mr Pruitt's official calendar.
"All of our time at the Vatican was spent with Cardinal Pell," Chmielewski told CNN.
Mr Pruitt's trip to Italy cost US taxpayers a reported $US120,000.
The New York Times published a new report shortly before Mr Pruitt's resignation on Thursday alleging how one of his senior schedulers, Madeline G Morris, was fired after questioning the practice of retroactively deleting meetings from the calendar, including from the Rome trip.
In another controversy earlier this year, federal records obtained under the Freedom of Information Act exposed emails detailing how a Washington-based consultant and former lobbyist helped arrange Mr Pruitt's planned August, 2017 trip to Australia
The trip did not go ahead because Hurricane Harvey struck Texas.
The proposed itinerary included potential meetings with Prime Minister Malcolm Turnbull, a visit to Uluru and a Bondi Beach walk.
Michael Brune, executive director of environmental group Sierra Club, said the emails "expose the fact that corporate lobbyists are orchestrating Pruitt's taxpayer-funded trips to push their dangerous agendas".
The long list of another controversies and scandals Mr Pruitt faced included attempting to purchase a used mattress from the Trump Hotel in Washington DC and seeking a "business opportunity" for his wife with the fast-food chain Chick-fil-A.