When in was announced that Oklahoma Attorney General Scott Pruitt was being nominated to head the Environmental Protection Agency, many conservationists and eco-friendly greens were abundantly appalled to find out one of the agency’s top critics was now being put in charge of it.

“The EPA has become a one-agency job killer, putting working people out of a job and increasing costs for everyone,” says former Florida Gov. Jeb Bush, an unlikely Donald Trump ally who went to bat for Pruitt in an op-ed published recently by CNN.

That describes overwhelming Republicans who have ventured far and away from the preservationist tendencies of party forefather Theodore Roosevelt. In an effort to create a more pro-business environment, Trump has criticized the EPA’s role in regulating industry standards in addition to the off-limits approach to mineral resources in our National Parks.

Here are three things to know about the EPA, opponent of Big Oil and fossil fuel interests:

It’s the largest federal agency in Washington

Under the guidance of President Nixon, the EPA was established to consolidate several federal bureaucracies into an agency that would then oversee licensing, implementation of environmental law, environmental research and development, assessment tests, and waste management.

Since then it has grown.

It focuses on the prevention (and correction of) pollution, under a law passed in 1990. It also leads coordinated cleanups, regulates nuclear facilities, oversees the Energy Star program for appliances and combats global warming through environmental justice programs. “Its ever-growing number of rules had cost the regulated community $180 billion at the twentieth century’s end,” according to Encyclopedia.com.

The EPA chief has been in charge of the president’s environmental agenda

America’s shift toward renewable energy really began under President Obama, following the 2010 Deepwater Horizon oil spill off the coast of Texas. It was EPA Administrator Gina McCarthy who’s responsible for implementing the White House plan for renewable energy, with an eye toward 10 gigawatts of clean energy on U.S. properties by 2020.

Since her time as the agency’s chief, McCarthy has said the “train has left the station” on America’s Clean Power Plan, and that it would be difficult to roll back regulations and defeat the forward progress the outgoing administrator had oversight of.

“I don’t think EPA’s only task is to regulate,” she recently told the Washington Post. “Our task is to reduce pollution with the best tools available.” The Trump Administration, meanwhile, has taken aim at the Clean Air Act and Clean Water Rule — both of which the EPA is responsible for enforcing.

Their main goal is maintaining healthy living standards in the environment

Following its creation after Earth Day in 1972, the EPA has seen a myriad of laws passed by Congress that it is responsible for upholding. The agency must work with scientists to identify any substance found in air, water, or the land and ensure companies and cities don’t contaminate the soil or drinking water with pesticides or other toxic waste.

It can be a hurdle for some companies to manufacture their products under these conditions. And yet, America has come a long way since Upton Sinclair published his muckraking work over the meat packing industry, back when one of five American children worked in factories and untold substances found their way into the local supermarket’s ground beef.

It’s not so easy to break the rules of common welfare now, and the EPA is in charge of making sure of that.