William J. Guste Jr., who served five consecutive terms as Louisiana’s attorney general and was the state’s longest-serving chief attorney, died July 24 at a retirement home in New Orleans. He was 91.

The death was confirmed by his son Bernard “Randy” Guste, who did not provide the cause.

The elder Guste worked in private practice for more than 20 years before being elected to the state Senate in 1968. He was elected Louisiana’s attorney general in 1972, the first of his five terms. He served until 1992.

Mr. Guste also was a former proprietor of Antoine’s Restaurant in New Orleans. The historic French Quarter restaurant was opened by his great-grandfather, Antoine Alciatore, in 1840. He and his brother, Roy Guste Sr., were the fourth generation to run Antoine’s, which bills itself as the nation’s oldest family-run restaurant.

Louisiana’s attorney general, James D. “Buddy” Caldwell (R), said in a statement that Mr. Guste “tackled everything from environmental issues to consumer fraud.”

Bernard R. Guste, left, proprietor of Antoine's Restaurant, stands next to his father, William J. Guste Jr., in the restaurant's main dining in New Orleans in 1999. William J. Guste Jr. passed away July 25, 2013. (Judi Bottoni/Associated Press)

Mr. Guste established an environmental law section in the Louisiana Department of Justice and was the state’s representative in legal challenges to laws restricting abortion and expanding the teaching of biblical creation in public schools. His work on lawsuits involving oil and gas royalties led to settlements worth hundreds of millions of dollars to the state, said Rusty Jabour, who served as his press secretary.

Mr. Guste also presided over the National Association of Attorneys General. In addition, President Ronald Reagan appointed him to the national Commission on Organized Crime, and he served on the national Environmental Enforcement Council.

Survivors include his wife of 65 years, Dorothy, and nine of his 10 children.