Edwin F. Kagin, the son of one minister and father of another, who saw religiosity creeping into the public domain and fought against it in a dual role as head lawyer and jester-provocateur for one of the country’s most militant atheist organizations, died on March 28 at his home in Union, Ky. He was 73.

The cause was undetermined, but he had a history of heart ailments, his sister Mary Kagin Kramer said.

Mr. Kagin was the national legal director of American Atheists, an organization founded in 1963 by Madalyn Murray O’Hair, who was instrumental in the Supreme Court decision that year banning school prayer. He was associated with the group for 40 years.

His lawsuits challenged references to “almighty God” in Kentucky state legislation, the placement of 12-foot-high crosses on highways in Utah, and plans to include a 17-foot-tall steel-beam remnant of the World Trade Center, in the shape of a cross, in the National Sept. 11 Memorial and Museum, which is scheduled to formally open in New York next month.