WASHINGTON – Leon G. Billings, a former aide to Maine Sen. Edmund Muskie and a key author of the Clean Air Act and other landmark environmental laws, has died.

Billings, 78, died Tuesday in Nashville, Tennessee, after suffering a stroke while visiting family.

Born in Montana, Billings moved to Washington in 1962 and had a 50-year career in politics and public policy. As the first staff director of the Senate Environment subcommittee, Billings was a primary author of the 1970 Clean Air Act, one of the first and most influential environmental laws in U.S. history and a foundation for current air pollution laws.

Billings also played a key role in the 1972 Clean Water Act, the primary federal law governing water pollution, and 1977 amendments to both the air and water pollution laws.

Billings served as Muskie’s environment adviser for more than a decade and later was the Democrat’s chief of staff in the Senate and when Muskie was secretary of state under President Jimmy Carter.

Billings also taught politics at the University of Southern California and served in the Maryland Legislature from 1991 to 2003, focusing on environmental issues.

He later ran a consulting firm and taught college courses on the Clean Air Act and other laws.

Tom Jorling, who was Republican staff director on the Senate subcommittee while Billings led the Democratic majority, said Billings “had tremendous skills legislatively and politically. He was respected and trusted by all members of the committee, majority and minority. His talent and skills led to the enactment of the foundational environmental laws of that era.”

Former Environmental Protection Agency administrator William K. Reilly, who worked in the Nixon White House when the clean air and water laws were signed, called Billings “an architect of the new order” who did “great work that the public health has benefited enormously from.”

Billings’ son, Paul, said his father learned the importance of advocating for social justice from his parents.

“There was no greater public health champion. Our air and water are cleaner and Americans are healthier because of Leon Billings,” said Paul Billings, senior vice-president of the American Lung Association.

Billings is survived by his wife, Cherry Billings, of Bethany Beach, Delaware, and three children. His first wife, former Maryland Del. Patricia Billings, died in 1990. Leon Billings was appointed to her seat before winning election in his own right.

Jorling said Billings was disappointed to see clean air and water laws come under attack from Donald Trump and congressional Republicans, but said the laws have survived previous attacks from the White House and Congress. Trump has called climate change a hoax and vows to cut back the role of the Environmental Protection Agency, which he describes as a job killer.

“Leon’s work helped prevent any wholesale efforts at eliminating or rolling back those statutes” in previous administrations, Jorling said. The current fight “would have been a new challenge for Leon.”

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AP Science Writer Seth Borenstein contributed to this report.