WASHINGTON – Long saddled with the label of "swing vote," U.S. Supreme Court Justice Anthony Kennedy has a new moniker that will travel with him into history: the court's strongest champion of gay rights.

His passionate majority opinion in the June 26 landmark United States v. Windsor, coupled with his similarly heartfelt rulings in Romer v. Evans in 1996 and Lawrence v. Texas in 2003, means that Kennedy has taken the lead role in the trilogy of Supreme Court rulings that turned the tide after the crippling gay rights defeat in 1986 in Bowers v. Hardwick.

"This will be the major part of his legacy, and I don't think he would have it any other way," said political scientist Helen Knowles, author of a 2009 book on Kennedy's jurisprudence, "The Tie Goes to Freedom."

"A hundred years from now, histories of the court will treat Justice Kennedy with respect to gay rights the way we think of Earl Warren with respect to racial equality," said Michael Dorf, a Cornell Law School professor and a former Kennedy clerk.

On the day Windsor was announced, Dorf went even further with his assessment of the justice when he blogged, "If Bill Clinton was 'the first black president,' Anthony Kennedy has now firmly secured his place in history as 'the first gay justice.'"

Kennedy's place in history is certain, but explaining why Kennedy has been so fearless and prominent on gay rights is less obvious.

Conservative on issues ranging from affirmative action to abortion, Kennedy is expansive on gay rights. In Romer, which struck down a Colorado initiative that barred legal protections for gays, Kennedy announced, "A state cannot deem a class of citizens a stranger to its law." In Lawrence, striking down anti-sodomy laws, Kennedy said that gays, like heterosexuals, "have the right to define [their] own concept of existence, of meaning, of the universe, and of the mystery of human life." In Windsor, Kennedy said the Defense of Marriage Act, which defined marriage as between one man and one woman under federal law, "writes inequality into the entire United States Code." And, he said, the law "singles out a class of persons deemed by a state entitled to recognition and protection to enhance their own liberty."

To Knowles, who teaches government at Skidmore College, Kennedy's opinion in Windsor was at once unsurprising and mysterious.

"Of all the areas of his jurisprudence, this is the most predictable part of it," she said. "But I'm not sure anyone can explain it fully."

'Modestly Libertarian Instincts'

Theories abound nonetheless. Commentator Andrew Sullivan on CNN last week pointed to Kennedy's Roman Catholicism. Despite the views of the Catholic hierarchy on gay rights, Sullivan said, many Catholics "care, as Jesus did, about the marginalized, and treating them with dignity."

Others note that Kennedy grew up in California—Sacramento, to be exact, where he knew then-Governor Earl Warren as a young man.

"He is a California establishment Republican with modestly libertarian instincts," professor Pamela Karlan of Stanford Law School told The Los Angeles Times last year. "He travels in circles where he has met and likes lots of gay people."

One of Kennedy's oldest friends, in fact, was Gordon Schaber, long-time dean of Sacramento's University of the Pacific McGeorge School of Law, where Kennedy has taught for decades. Schaber often turned up on Kennedy's annual financial-disclosure forms, because he gave Kennedy gifts of expensive dress shirts. Time magazine last year reported that Kennedy learned that Schaber, who died in 1997, was "secretly gay."

Larry Levine, a McGeorge professor who is gay and who knows Kennedy, said his sexuality has never come up in his discussions with the justice, and he doubts Kennedy and Schaber discussed Schaber's sexual orientation either.

"With people of that generation, no one talked about it," Levine said in an interview.

Studies have shown that having gay friends influences a straight person's attitudes about homosexuality, but Levine said "that does not explain a lot" about why Kennedy has become a champion of gay rights.

"He is a very kind, caring person, but he is not going to base his decisions on his friendships," Levine said.

Then, there is an oft-discussed side to Kennedy's personality: a certain grandiosity that sometimes comes across in his writing, and his desire to be popular in liberal circles. It used to be called the "Greenhouse effect"—moving to the left to win the favor of Linda Greenhouse, the former New York Times Supreme Court correspondent, and other presumed liberal commentators.

"Does he like being celebrated? Maybe," Levine said. "I don't think you can be a justice for 25 years and be humble. But if he wanted to be celebrated at parties in Georgetown, he wouldn't be part of these other decisions."

Levine referred to Kennedy's votes last month in the affirmative action case Fisher v. University of Texas at Austin and the voting rights case Shelby County v. Holder. In both cases, Kennedy took a dim view of programs long favored by traditional civil rights groups. Similarly, in the same week he announced Lawrence v. Texas in 2003, Kennedy articulated a restrictive view of affirmative action in Grutter v. Bollinger.

Knowles, too, sees "a little bit of pomposity" in Kennedy's writings. In describing the difficulty of deciding hard cases, Kennedy once told an interviewer: "Sometimes you don't know if you're Caesar about to cross the Rubicon or Captain Queeg cutting your own tow line."

But when it comes to gay rights, Knowles said, "he is as honest as they come." She said that from his earliest days as a judge, Kennedy has had a "basic egalitarian instinct" that informs his decision-making, "a concept that everyone should be treated the same."

In a 1996 New Yorker profile of Kennedy, his long-time friend and former California governor and senator Pete Wilson said of Kennedy, "I think it strikes him as terribly unfair that anyone's individual potential should be in any way limited by their being classed as a member of a group, and treated in accordance with their group membership, rather than what they deserve to receive as individuals."

That sense of injustice is at full blossom for Kennedy, Knowles said, when it comes to government interference with an individual's private sexual activity.

"He clearly feels very strongly that sexual orientation is an important part of a person's makeup. It brings out in him almost poetic language," Knowles said.

Kennedy has a reputation for agonizing over decisions, but he once said the result in Lawrence was so clear to him that he wrote the decision in a weekend, according to Jan Crawford in her 2007 book "Supreme Conflict."

Individual Dignity

But affirmative action and the Voting Rights Act are tougher calls for Kennedy, representing government interference based on group membership rather than individual respect, according to Knowles.

In her book, Knowles wrote, "Kennedy believes that an individual is stripped of his or her dignity by government treatment—positive or negative—that is driven by the race of that individual."

Suzanne Goldberg, a Columbia Law School professor and an expert on the court's gay rights jurisprudence, also has sought to reconcile Kennedy's gay rights support with his sometimes stingy views on the rights of other minorities.

"Justice Kennedy's opinions in this area reflect a pull-yourself-up-by-your-bootstraps vision of equality," Goldberg said. "Justice Kennedy's gay rights opinions are consistent with an old and well-settled tradition in American anti-discrimination law of striking down direct attacks on vulnerable minorities. These laws, on their face, are a direct attack on a minority's dignity and humanity."

But when it comes to other civil rights issues, Kennedy has a different perspective, Goldberg said.

"The harm caused by rejecting the Voting Rights Act or making race-based affirmative action more difficult to sustain requires a more contextual evaluation that responds to the realities of 21st century discrimination, which are usually less explicitly hostile than what we saw in [the Defense of Marriage Act] or what we saw in Texas' homosexual conduct law and Colorado's anti-gay amendment," said Goldberg.

Levine sees it similarly.

"He has a theory of equality, not difference; different treatment to him is demeaning," Levine said.

Levine thinks gay rights has become Kennedy's signature cause partly for another reason as well. The angry reaction to Kennedy's gay rights views—from the public in hate mail, as well as from colleague Antonin Scalia in dissents—has "pushed Kennedy more toward the progressive side. It has been a great gift to LGBT rights that Scalia has been so vitriolic toward Justice Kennedy."