Walter Dellinger III, a celebrated constitutional scholar who served as acting U.S. solicitor general during the Clinton administration, counselor to presidents, and later head of the Supreme Court and appellate practice at O’Melveny & Myers, died Wednesday at the age of 80.

Dellinger most recently served as a member of the Biden administration’s special commission studying the Supreme Court and potential changes in its operation. He also was part of a three-member team of former solicitors general during the 2020 presidential campaign that worked on behalf of then-candidate Joe Biden to prepare for potential attempts to delegitimize the election. With him in that effort were Wilmer Cutler Pickering Hale and Dorr partner Seth Waxman and Munger, Tolles & Olson partner Donald Verrilli Jr.

Less than two weeks before his death, Dellinger wrote an opinion piece in The New York Times explaining why it is important that a Black female be nominated to the Supreme Court. The article was quintessential Dellinger, writing about the institution he had devoted a lifetime to studying, serving and caring about.

The Supreme Court, he wrote, “exercises immense power to issue decisions that affect and bind all Americans. For that power to be legitimate, and for Americans to continue placing faith in the court, its members must be representative of all of America.”

Tributes to Dellinger flowed across social media platforms almost immediately after news broke of his death. His former O’Melveny partner and now White House chief of staff Ronald Klain, tweeted: “Mourning the loss this morning of the great @walterdellinger—wise counselor, steadfast advocate, teacher and public servant—a great mentor to me and so many others—and a kind friend.”

O’Melveny’s Chair Bradley Butwin said the firm was “heartbroken” by Dellinger’s passing.

“To say he was a ‘living legend’ doesn’t begin to capture the greatness of his intellect, heart and spirit,” Butwin said in a statement. “In both government service and private practice, Walter’s commitment to social justice and equality was unmatched. He was a giant in the law—as a practitioner, a scholar, a counselor and a statesman—and his legal accomplishments will endure for generations.”

Butwin also remembered Dellinger as a caring family man and a devoted mentor of legal talent.

“There is a remarkably long list of lawyers in academia, in government, in business, at law firms, at nonprofits, and on the bench who Walter helped to find their place,” Butwin said. “As he mentored scores of young lawyers—including many of America’s great jurists—he also took the time to weigh in on many of the most pressing issues facing our society. We take comfort from knowing how much he loved our firm and the enduring impact he had on all of us. We are all better off for his wisdom, kindness, and contributions.”

“Walter Dellinger was a lion of the law, the legal profession, and legal education,” said Kerry Abrams, the dean of the Duke University School of Law, where Dellinger was a longtime professor. “A cherished member of the Duke Law School faculty for more than five decades, he was a true intellectual as well as being a generous and big-hearted colleague, mentor, and friend. Our community will miss him terribly.”

U.S. Supreme Court Justice Elena Kagan also remembered Dellinger, saying in a statement: “Walter was a great mentor and friend to me. He gave the best advice when I became solicitor general, sharing everything he knew about the job. He was generous and kind, and he made everyone he dealt with feel 10 feet tall. He was a phenomenal lawyer with an endless string of accomplishments, but he always gave the credit to others. I’ll miss his sense of humor, his clear-eyed optimism, and his passionate engagement with the world of law.”

And Justice Stephen Breyer said in a statement: “Walter Dellinger was a great lawyer and a valuable public servant. He was thoughtful. imaginative, and had a very good sense of humor. His positive contribution to law and to the rule of law in this country will be long remembered.  Like my colleagues and all who knew him, I shall miss Walter very much.”

Attorney General Merrick Garland recalled working with Dellinger early in Garland’s career at the Justice Department. Garland said it was “difficult to know where to begin in remembering someone who lived as fully and gave of himself as generously as Walter did.”

“Walter approached the law not as a career, but as a calling,” Garland said in a statement. “He believed it was his privilege to be able to use the law to make our democracy work better for everyone. He was a tireless advocate on behalf of those with whom he worked, and on behalf of the American people for whom he worked. He did not hesitate to lend his voice in service of lifting up the voices of others. His work had an enormous impact on all of us at the Justice Department, and on the lives of millions of people he would never know.”

Former Judge J. Michael Luttig tweeted, “Walter Dellinger was a wonderful human being, a spectacular lawyer and counselor, and a friend. I am shocked and saddened to hear this news.”

“Walter Dellinger was a champion for the progressive promise of our Constitution’s text, history, and values,” Elizabeth Wydra, president of the Constitutional Accountability Center, said in a statement. “From his years as a law professor, to his service in government, to his leadership of the Supreme Court practice of one of the nation’s leading law firms, Walter had a tremendous legal career. And throughout his more than 50 years in the law, Walter worked tirelessly to make America more perfect. Making his loss that much more difficult, he was also just a delightful person. He will be dearly missed.”

Dellinger graduated from Yale Law School and clerked for U.S. Supreme Court Justice Hugo Black during the court’s 1968-69 term.

After serving as a White House adviser on constitutional issues in the early months of the Clinton administration, Dellinger was nominated to be an assistant attorney general in charge of the Justice Department’s Office of Legal Counsel, a role he held from 1993 until 1996. The office is responsible for drafting legal opinions about issues under discussion in the executive branch.

He was then named acting solicitor general for the 1996-97 Supreme Court term. He argued a total of 24 cases before the justices, nine cases during his tenure as acting solicitor general.

In 2008, the District of Columbia asked him to argue on its behalf in the landmark Second Amendment case, District of Columbia v. Heller, which he subsequently lost in a 5-4 decision.

As was his practice, Dellinger biked to the court that chilly March morning. He said riding his bike to the court helped him “clear his head.”

In addition to the Second Amendment case, Dellinger had two additional major arguments that term: Exxon Shipping Co. v. Baker and Morgan Stanley Capital Group v. Public Utility District No. 1.

Dellinger was a longtime professor at Duke’s law school, where he taught continuously from 1969 until 1993.

Dellinger’s wife, Anne, a retired member of the University of North Carolina School of Government, died last year at age 80. His son, Hampton Dellinger, is currently serving as assistant attorney general for the Office of Legal Policy, the Justice Department office that assists with judicial nominations and advises the attorney general on policy matters.