When John Paul Stevens was nominated to the Supreme Court in the 1970s, he steeled himself for a bombshell from his past as a Seventh Circuit judge. There, he’d authored a dissent that claimed it was legal to prevent married women from becoming flight attendants at United Airlines. That conservative stance infuriated members of the women’s movement and worried Stevens’s supporters, who warned him to be ready to explain his seemingly retro opinion during a time of increasing civil rights for women.

Was Stevens too conservative for the Supreme Court of a society that had veered sharply to the left?

As it turned out, the judge wasn’t questioned about the dissent during his confirmation hearings. And those who worried he’d push the Supreme Court too far to the right were in for a surprise. Appointed by a Republican president, the Associate Justice got off to a conservative start. But, perhaps more so than any modern Supreme Court justice, Stevens embodied change. As the third-longest-serving member of the Supreme Court, he revised his own views on many of the nation’s most pressing issues.

At the beginning of his Supreme Court career, he upheld the Second Amendment, the death penalty and railed against affirmative action. By the end, he had done an about-face on all three. His most influential majority opinions decriminalized homosexual activity and paved the way for gay marriage (Lawrence v. Texas), upheld the separation of church and state (Wallace v. Jaffree) and affirmed the legal rights of Guantanamo Bay detainees (Rasul v. Bush_)._ He even signed on to the Court’s controversial affirmation of a woman’s right to an abortion in Planned Parenthood v. Casey.

He also made a name for himself through his vigorous dissents—often solitary—against conservative victories like Bush v. Gore, which settled the 2000 presidential election in Bush’s favor, and Citizens United v. FEC, which prohibited the government from limiting independent political expenditures on behalf of political campaigns. After his retirement, he called for a repeal of the Second Amendment, calling its premise “a relic of the 18th century.”

The more conservative the Supreme Court got, fueled by changes in the Republican Party, the more liberal Stevens became.

Before he joined the Supreme Court, Stevens made a name for himself in private practice. It took a pair of scandals to bring Stevens, an antitrust attorney, to national prominence. He was general counsel for a special committee the Illinois legislature appointed to investigate claims that two Illinois Supreme Court judges had accepted bribes from a bank. Though taking on members of the state’s highest court was a difficult gamble for a working attorney, Steven’s dogged work exposed the judges’ acceptance and concealment of money they should not have taken.

The committee’s revelations brought Stevens to the attention of President Nixon, who appointed him to the U.S. Court of Appeals for the Seventh Circuit, which is based in Chicago, in 1970. Then Nixon resigned in the wake of the Watergate scandal—and when Justice William O. Davis retired, Nixon’s successor, Gerald Ford, faced a thorny situation. It was the first Supreme Court vacancy since the president’s resignation, and Ford worried about a divisive nomination in a nation still reeling from the scandal.

Stevens seemed like the ideal candidate: He had no personal ties to Nixon and had never worked in his cabinet, his name was closely associated with impartiality and the willingness to challenge corruption, and he was a Republican. Ford nominated him to the Supreme Court in November 1975. Just 19 days later, Stevens was confirmed.

At first, Stevens’ conservative views made an impact on national law. As a new justice, he sided with the majority in Gregg v. Georgia, a landmark case that reinstated the death penalty after a previous case that had struck down the practice throughout the United States. Stevens also entered the court as one of affirmative action’s most vocal enemies. “As of 1980,” writes J.P. Scanlan, “no member of the Court seemed more opposed to race-conscious measures than Justice Stevens.”

But during his time on the court, Stevens found himself defending liberal causes again and again, as the makeup of the Court moved farther right—like the country at large—as Republican presidents nominated hard-line justices like Antonin Scalia. And over the years, the judge’s own opinions on issues changed, pushing him further and further from his initial stances.

Perhaps the most dramatic of the judge’s shifts was his attitude toward the death penalty. Though Stevens claimed that his views had not really changed, legal scholar Christopher E. Smith argues that Stevens’s experience investigating corruption made the judge acutely aware of judicial fairness. It pushed him to question how death penalty cases were prosecuted and whether they were skewed against defendants who were treated unfairly by law enforcement and the courts.

Over time, Stevens went from defending the death penalty to skewering it. Too often, he argued, the death penalty was applied in a discriminatory way, playing an “unacceptable role” in capital cases. Eventually, he concluded that the death penalty was cruel, unusual and not constitutionally acceptable. It concurred no benefit on society, he wrote, and could not be justified. Later in life, he stated that reinstating the death penalty in 1976 was his one regret from his tenure on the Supreme Court. He also said that District of Columbia v. Heller, a case that formally recognized individuals’ rights to own firearms, was the single worst decision of his tenure.

After initial strikes against affirmative action, writes legal scholar Diane Marie Amann, he began to think of the practice of affirmative action as a way to redress past wrongs and ensure a future that enabled people to take full advantage of their skills. Eventually, writes Amann, Stevens came to see affirmative action as “among those measures that the Constitution allows an equally impartial government.”

In later years, Stevens was openly critical of his colleagues’ abandonment of affirmative action. In Parents Involved in Community Schools v. Seattle School District No. 1, he wrote a scathing dissent that claimed the Supreme Court was no longer faithful to the Brown v. Board of Education decision that ended segregation in public schools. “It is my firm conviction that no Member of the Court that I joined in 1975 would have agreed with today’s decision,” he wrote.

Stevens led the majority in decisions like Atkins v. Virginia, in which the Court ruled that executing people with intellectual disabilities is cruel and unusual punishment and violates the Eighth Amendment. The decision narrowed the Court’s view on when the death penalty can be applied.

By the time he retired in 2010, Stevens had authored liberal majority opinions in a variety of landmark cases, including Lawrence v. Texas (which struck down laws against homosexual activity), Wallace v. Jaffree (which struck down a state-mandate minute of silence for prayer in Alabama schools) and Rasul v. Bush (which affirmed Guantanamo Bay detainees’ right to petition for habeas corpus). And in 1992, he was part of the majority in Planned Parenthood v. Casey, a case that upheld the right to an abortion established in Roe vs. Wade. “A woman who decides to terminate her pregnancy is entitled to the same respect as a woman who decides to carry the fetus to term,” he wrote in his concurrence.

Though Stevens had initially been seen as a safe pick for a Republican president, his opinions eventually became so liberal that they infuriated Republicans. In turn, Republicans redoubled their attempts to control judicial nominations in the hopes of forcing the Supreme Court into a more conservative mold. “Stevens and his long tenure help explain why conservatives have become so focused on judicial nominations,” writes New York Magazine.

Despite his unexpectedly liberal stances, Stevens claimed he himself was not a liberal. “As part of my general politics, I’m pretty darn conservative,” he told the New York Times in 2007. Instead, he said, he considered cases on their individual merits.

As he told USA Today after his 2010 retirement, “I was trying to apply the law in a sensible way."