AQUILINO “Nene” Pimentel, Jr., father of the Local Government Code and a former Senate president and opposition leader who fought the dictatorship in the 1970s, has died. He was 85.

Mr. Pimentel, who was hospitalized last week due to lymphoma and pneumonia, died at 5 a.m. on Sunday, his son Senator Aquilino “Koko” Pimentel III said.

The former senator was one of the leading opposition leaders when the late dictator Ferdinand E. Marcos declared martial law in 1972. He was imprisoned several times for opposing martial rule by Mr. Marcos, who was toppled by a popular uprising in 1986.

Mr. Pimentel co-founded the country’s ruling Partido Demokratiko Pilipino–Lakas ng Bayan (PDP-Laban) and served as Senate president from 2000 to 2001.

“His long and storied career as a statesman is replete with moments of moral courage as he stood firm against the oftentimes cruel realities of politics and history,” Vice President Maria Leonor G. Robredo said in a statement. “May we all draw inspiration from his example to show the same courage and principle during these challenging times.”

Mr. Pimentel was born on Dec. 11, 1933 to Aquilino E. Pimentel Sr. and Petra Quilinging. He married Lourdes de la Llana on April 30, 1960 and they had six children — Aquilino Martin “Koko” III, Gwendolyn Petrecia, Ma. Petrina, Aquilino Justinian IV, Teresa Lourdes and Lorraine Marie, according to his official website.

He finished his law degree at Xavier University in 1959 and practiced the profession from 1960 to 1980. He authored and co-sponsored key legislative measures including the Local Government Code of 1991, the Cooperative Code, as well as the bill that created the Autonomous Region in Muslim Mindanao.

Mr. Pimentel was a relentless critic of the Marcos regime and was often seen with the late Benigno S. Aquino Jr.’s widow, Cory, during opposition rallies. At one point, Cory asked him to be her running mate in snap elections called by Mr. Marcos in 1986, to which he agreed. He later stepped aside at the last minute to give way to Salvador “Doy” Laurel.

Before being elected senator in June 1987, Mr. Pimentel served as mayor of Cagayan de Oro City in Mindanao from 1980 to 1984.

He became minister of Local Government under then President Corazon “Cory” C. Aquino, before he authored the Local Government Code in 1991, which devolved functions including health care from the national government.

“Today, our country has lost a true patriot, a freedom fighter and a champion of democracy, human rights and local governance,” Senator Franklin M. Drilon said in a statement.

“I lost not just a colleague whom I shared nine colorful years in the Senate, but a true friend who I respect and admire for his service to the nation and our countrymen,” he added.

Mr. Pimentel was an ally of former President Joseph E. Estrada before his six-year-term was cut short by another street uprising in 2001. He was Senate president when the chamber tried Mr. Estrada for corruption and was part of the minority that voted in January 2001 to open an envelope supposedly containing details of the accused’s secret bank accounts.

Mr. Pimentel was also a member of the Duterte administration’s consultative committee reviewing the 1987 Constitution and drafting a federal charter.

Mr. Pimentel was “not only one of our most experienced and accomplished civil servants, he is also one of the greatest defenders of freedom and democracy in the history of our country,” Senator Risa N. Hontiveros-Baraquel said in an emailed statement. “His greatness was only eclipsed by his love for this nation and its people.” — Vince Angelo C. Ferreras