President Donald Trump announced on Thursday that his embattled Environmental Protection Agency chief, Scott Pruitt, had resigned.

Pruitt has for months faced increasing pressure to resign amid numerous reports about his ethically questionable leadership of the agency.

Pruitt joins a long list of senior officials who have either been fired or resigned from the Trump administration.

President Donald Trump announced Thursday that his embattled Environmental Protection Agency chief, Scott Pruitt, had resigned.

In a series of tweets, the president thanked Pruitt for his service and announced that Andy Wheeler, the EPA's deputy head who was formerly a coal lobbyist and Senate staffer, would take over as acting administrator.

"I have accepted the resignation of Scott Pruitt as the Administrator of the Environmental Protection Agency," Trump said. "Within the Agency Scott has done an outstanding job, and I will always be thankful to him for this."

He continued: "I have no doubt that Andy will continue on with our great and lasting EPA agenda. We have made tremendous progress and the future of the EPA is very bright!"

In a resignation letter made public shortly after Trump's tweets, Pruitt said that the decision to resign was a difficult one but that the "unrelenting attacks" on him and his family forced him to leave the role.

"It is extremely difficult for me to cease serving you in this role first because I count it a blessing to be serving you in any capacity, but also, because of the transformative work that is occurring," he wrote. "However, the unrelenting attacks on me personally, my family, are unprecedented and have taken a sizable toll on all of us."

Pruitt, now the shortest-serving chief in the EPA's history, lavished praise on the president and argued that he had been able to advance Trump's agenda "beyond what anyone anticipated at the beginning" of his administration.

"I believe you are serving as President today because of God's providence," Pruitt said in the letter. "I believe that same providence brought me into your service. I pray as I have served you that I have blessed you and enabled you to effectively lead the American people."

Eric Lipton, a New York Times reporter who has covered Pruitt extensively, pushed back on Pruitt's suggestion that the negative reports on his leadership were personal.

"Not a single story we wrote about Scott Pruitt and his tenure at the EPA-by me or my colleagues at The NYT-was personal," Lipton tweeted. "It was about transparency, accountability, & governance. Pruitt likes to call it 'The Rule of Law' He just gave us an enormous amt of material to write about."

Pruitt is the subject of at least 13 federal investigations into his behavior and decision-making at the agency, including those related to his frequent first-class flights and copious spending on personal security. Both Democrats and Republicans have urged Pruitt to resign amid months of scandalous reports of potential ethics violations.

Pruitt, the former Oklahoma attorney general, was one of the most controversial members of the Trump administration and brought a deeply conservative agenda to the agency. A climate-change skeptic, Pruitt has close ties to the fossil-fuel industry and spent years suing the EPA over policies he argued constituted federal overreach, including ozone and methane-emissions rules and coal-plant regulations.

The administrator's resignation was celebrated by his critics on Thursday. He joins a long list of senior officials who have either been fired or resigned from the Trump administration.

"Good bye Scott Pruitt, the worst Administrator in EPA history and perhaps the word cabinet member ever," said Richard Painter, President George W. Bush's chief ethics lawyer. "Fake science, fake ethics and fake religion (complete with a cultish theology of planet destruction) all rolled into one."

Citizens for Responsibility and Ethics in Washington, a top government watchdog, released a one-word statement in response to Pruitt's resignation.

"Good," the group said.

A long list of ethics scandals

News reporting and federal investigations into Pruitt's practices at the EPA have exposed an array of allegations of abuses, some of which are listed below: