Much has been said about the legal duo who convinced a federal judge that California’s ban on same-sex marriage is unconstitutional: Ted Olson and David Boies. But Olson can find another close friend on the opposite side of the courtroom: Charles Cooper, a partner at Cooper & Kirk in Washington.

“He’s a marvelous lawyer and a good friend,” Olson said of Cooper, who is defending Proposition 8. They worked together in the Justice Department under President Reagan, and Cooper was Olson’s successor as assistant attorney general in the Office of Legal Counsel in 1985.

Cooper’s team of about a dozen lawyers represents ProtectMarriage.com, the entity behind Proposition 8, and four additional proponents of the ballot initiative. The team includes lawyers representing the Alliance Defense Fund, a legal organization in Scottsdale, Ariz., focused on “religious liberties,” and Andrew P. Pugno of the Law Offices of Andrew P. Pugno in Folsom, Calif., a trusts and estates attorney who is general counsel of ProtectMarriage.com.

At trial in San Francisco in January, the team sought to rebut claims that Proposition 8 violated the rights of gays and lesbians under the due process and equal protection clauses of the Fourteenth Amendment. They argued that the state has an interest in defining marriage as between a man and a woman to ensure that procreation and child-rearing occur within a stable household.

On Aug. 4, U.S. District Judge Vaughn Walker, calling marriage a “fundamental right” that is not based on gender, ruled that Proposition 8 is unconstitutional. On Aug. 16, the U.S. Court of Appeals for the 9th Circuit granted a stay of the ruling and set arguments for December.

Cooper’s opening brief is due on Sept. 17. He declined to discuss his arguments, but his stay cited numerous precedents, from both the U.S. Supreme Court and the 9th Circuit, holding that restricting marriage to opposite-sex couples serves a governmental interest. He also defended ProtectMarriage.com’s standing in the case and challenged Walker’s standard of review.

Cooper and his firm are no strangers to high-profile cases. He has represented the National Rifle Association in numerous constitutional challenges and several former unindicted lacrosse players at Duke University who sued the school, the city of Durham, N.C., and others for invasion of privacy and emotional distress following the bogus rape case brought against three of their teammates. The Proposition 8 case is “in a class by itself,” Cooper said. “It’s a momentous legal and constitutional issue and a public policy issue about which almost everyone in the country cares something about — and many, many people care passionately about.”

Cooper has no plans to change the legal team as the case goes to appeal. He faces a formidable foe: He and Olson not only are experienced appellate specialists but also are friends of the Supreme Court’s most conservative justices. They “see each other pretty regularly” on social occasions — although not so much lately, Cooper said. “That’s been because we’ve been so busy. This case is one on which we profoundly disagree, so we obviously have agreed to disagree about it.”

Contact Amanda Bronstad at abronstad@alm.com.