Scott Pruitt, the former Oklahoma attorney general who relentlessly pursued President Trump’s promises of deregulation at the Environmental Protection Agency, resigned Thursday after a cascade of controversies over his lavish spending, ethical lapses and controversial management decisions finally eroded the president’s confidence in one of his most ardent Cabinet members.

Pruitt’s reputation as a dogged deregulator and outspoken booster of the president allowed him to weather a litany of ethics scandals in recent months, including questions about taxpayer-funded first-class travel, a discounted condo rental from a D.C. lobbyist and the installation of a $43,000 soundproof phone booth in his office.

But revelations about his behavior continued to mount, including reports that he repeatedly enlisted subordinates to help him search for housing, book personal travel and even help search for a six-figure job for his wife. That quest included setting up a call with Chick-fil-A executives, in which he discussed her becoming a franchisee, as well as outreach to a conservative judicial group that eventually hired Marlyn Pruitt.

In recent weeks, an exodus of trusted staffers left Pruitt increasingly isolated, and some once-loyal Republican lawmakers wearied of defending him. Investigators on Capitol Hill had summoned current and former EPA aides for questioning, as part of the more than dozen federal inquiries into Pruitt’s spending and management of the agency.

On Thursday, President Trump called Pruitt’s top deputy, Andrew Wheeler, to inform him that he would be taking the helm of the agency, according to an individual who spoke on the condition of anonymity because of the sensitivity of the matter.

Soon after, Trump announced in a two-part tweet that he had accepted Pruitt’s resignation. “Within the Agency Scott has done an outstanding job, and I will always be thankful to him for this,” Trump wrote.

White House chief of staff John F. Kelly, who traveled with Trump to a political rally in Montana on Thursday, had for months privately groused about Pruitt’s conduct and pushed for his removal during West Wing meetings, according to White House officials who were not authorized to speak publicly. But the timing of Thursday’s move took even some White House officials by surprise, as the president had closely guarded the decision.

In a resignation letter released by the EPA, Pruitt wrote that it had been “a blessing” to serve under Trump and undertake “transformative work at EPA. But he added that “the unrelenting attacks on me personally, my family, are unprecedented and have taken a sizable toll on all of us.”

He signed the letter, “Your Faithful Friend, Scott Pruitt.”

Wheeler , a former Senate staffer and EPA employee who spent the past decade representing coal, mining and other energy companies, will become acting administrator on Monday, Trump tweeted.

The departure marked a precipitous fall for Pruitt, who during his roughly 16 months in office took steps to reverse more than a dozen major Obama-era regulations and overhauled key elements of the agency’s approach to scientific research. For months he had ranked as a personal confidant and influential policy adviser to the president, commiserating with Trump over negative stories and indiscreet aides while praising the commander in chief for his intelligence and political acumen.

As scrutiny of Pruitt grew in recent months, Trump initially stood by his EPA chief. The president tweeted in early April that he was “doing a great job,” despite revelations about a $50-a-night condo rental from a lobbyist, large raises for top aides and dozens of first-class flights and costly travel funded by taxpayers. Trump publicly defended Pruitt and praised his job performance as recently as early June.

Pruitt also endured a series of contentious hearings recently on Capitol Hill, admitting little culpability as lawmakers in both parties grilled him about his ethics and spending decisions.

But the EPA leader continued to be dogged by bad publicity, with a litany of alleged spending excesses that current and former aides shared with congressional lawmakers. The Government Accountability Office found that he violated spending laws by installing a $43,000 soundproof phone booth in his office — one of the more than a dozen federal inquiries launched into his management and expenditures.

The Washington Post reported that a lobbyist had helped arrange Pruitt’s $100,000 trip last December to Morocco, only to later receive a $40,000-a-month contract to promote that country’s interests.

Documents obtained under the Freedom of Information Act showed the same sort of pattern for a visit the administrator wanted to make to Australia. That travel was canceled at the last minute, as was a trip to Israel, which had been lined up in part by casino magnate and Republican megadonor Sheldon Adelson.

Those same documents contained emails that showed Pruitt used his official position to line up a call with an executive at Atlanta-based Chick-fil-A, during which he raised the prospect of his wife getting a coveted franchise.

Combative and unapologetic, Pruitt spoke with the rapid-fire delivery of a trial lawyer when outlining his policy positions or addressing audiences. While serving as Oklahoma’s attorney general, he made a name for himself in conservative circles by suing the EPA 14 times. And after taking over the EPA, he spent the bulk of his time meeting privately with industry leaders regulated by his agency, including top executives from the fossil fuel, agriculture and chemical sectors.

In the early months of the Trump administration, when other Cabinet members were struggling to recruit deputies and navigate their departments, Pruitt was already unraveling federal restrictions on greenhouse-gas emissions and toxic waste discharge from coal-fired power plants. He declined to ban a commonly used pesticide linked to potential neurological brain damage in fetuses, as the agency had previously proposed.

Most prominently, he pushed Trump to announce a U.S. withdrawalfrom the landmark Paris climate accord. He not only questioned the science of climate change but also the overwhelming scientific consensus that human activity is the primary contributor to global warming.

The moves, coupled with Pruitt’s penchant for secrecy, made him a lightning rod for controversy. He refused to release his schedule in advance or transcripts of his speeches to industry groups. He installed biometric locks on doors and constructed the soundproof phone boothsteps from his office.

From his third-floor, wood-paneled suite, Pruitt largely insulated himself from career staff, many of whom had worked to craft the policies he sought to dismantle. Meanwhile, through buyouts and a hiring freeze, he proudly shrank the EPA’s workforce to levels not seen since the 1980s.

Pruitt unrelentingly steered the agency in the direction long sought by those being regulated, a shift he defended as providing regulatory certainty, handing greater power to states and saving companies money in compliance costs.

Critics described his approach as nothing short of an assault on the agency’s mission, its employees and on science. Supporters applauded his willingness to wrangle an agency many conservatives view as prone to overreach and, as Pruitt recently said, “a bastion of liberalism.”

The administrator’s fervor and stamina elevated his profile significantly. At one point, Pruitt was viewed as a contender for attorney general if the president decided to fire Jeff Sessions, and he spoke privately with others about climbing the ranks of Trump’s Cabinet.

Pruitt, who had considered running for Oklahoma governor before joining the administration, made a point of meeting with GOP activists and addressing large organizations that could help further any future political ambitions. He delivered the keynote speech at the Conservative Political Action Conference’s annual gathering in February, a slot often reserved for presidential contenders

When asked at CPAC what stood out as his proudest moment as head of the EPA, he cited Trump’s decision to pull out of the Paris climate agreement — a decision that represented a win for Pruitt over Trump’s own daughter and son-in-law, Ivanka Trump and Jared Kushner.

“The president showed tremendous fortitude, tremendous courage to stand in the Rose Garden in June and say, ‘You know what. I’m going to put America first,’ ” Pruitt told the audience.

In recent months, however, Pruitt’s favor and credibility within the administration began to unravel. Even as he continued to announce far-reaching actions to scrap or scale back regulations, scrutiny over his ethical decisions and profligate spending began to overshadow his actual policies.

In February, The Washington Post detailed how Pruitt had routinely flown first-class and stayed in high-end hotels on dozens of trips during his first year, racking up hundreds of thousands of dollars in taxpayer-funded expenses. While the EPA said such travel arrangements were necessary given the elevated number of threats to Pruitt’s security, the revelations led to a wave of criticism about his spending and inquiries from lawmakers and government investigators.