Scott Pruitt's time as Environmental Protection Agency chief was dogged by questions about his extravagant spending habits and calls for him to step down. On July 5, the embattled administrator tendered his resignation — and EPA deputy administrator Andrew Wheeler will fill in, President Trump said.

The Senate confirmed Wheeler as second-in-command at the agency with a 53-45 vote in April.

While rumors of Pruitt's eventual departure swirled, Wheeler kept cool and assured the public he had no interest in filling the role as chief.

“While that’s flattering, I am not thinking about it, no,” Wheeler told the Washington Examiner in late June. “I could have put my hat in the ring for the administrator. I wasn’t interested in that. I am still not interested in that."

Trump said Wheeler would "assume duties" as acting administrator of the EPA on July 9.

"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!" Trump tweeted on July 5.

Here are 3 things you need to know about the interim EPA chief before he officially changes roles.

He was a major coal lobbyist

A former coal industry lobbyist, Wheeler helped lead an industry fight against regulations aimed at protecting Americans' health and addressing climate change. Many in the industry argued that the regulations would stifle business.

Throughout his decades-long career, Wheeler has reportedly lobbied for at least 20 different companies, including Sargento Foods Inc., Whirlpool Corporation, and Xcel Energy, among others.

During his time as a lobbyist, Wheeler worked alongside Interior Secretary Ryan Zinke to reduce the Bears Ears National Monument in Utah by 85 percent and reserve a piece of the land for uranium mining, Fortune Magazine reported.

In recent years, Wheeler has lobbied for Energy Fuels Resources Inc. and Murray Energy Corporation, which is run by longtime Trump supporter Robert Murray, who spent roughly $300,000 on the president's inauguration, according to The New York Times.

He's had a 20-year career in Washington

Wheeler worked for the EPA in the early 1990s, focusing on chemicals and toxic substance-related issues during the Bush and Clinton administrations.

He later transitioned into the role of staff chief of the Senate Environment Committee and served as counsel to Sen. James Inhofe, R-Okla.

He co-led law firm Faegre Baker Daniels' energy and natural resources team

Wheeler joined the international law firm Faegre Baker Daniels after his stint at the Senate Committee on Environment and Public Works.

During his time at the firm, he helped counsel a variety of clients on "comprehensive legislative, regulatory and operational strategies," the firm states on its website.

He worked on "every major piece of environmental and energy-related legislation" before Congress over the span of a decade, ProPublica reported.

“Andrew has served our firm with distinction. His extensive experience has benefited our clients and we wish him well as he returns to government," FaegreBD consulting chair Dave Zook said in an online statement after Wheeler's confirmation.

The Associated Press contributed to this report.