When Anthony Kennedy was nominated to the Supreme Court by President Ronald Reagan in 1987, he was portrayed as a balanced arbiter but overall a reliable conservative. But almost 26 years after his confirmation, Kennedy has evolved into a more complex and nuanced justice than Reagan likely ever anticipated, routinely siding with his liberal-leaning colleagues on civil liberty and gay rights issues.

Yet Kennedy hasn't strayed from his ideological moorings on many other hot-button topics, consistently delivering conservative rulings in cases relating to affirmative action, organized labor, campaign finance and gun control.

As the Supreme Court kicks off its 2013-14 term, Kennedy is expected to be the decider on many 5-4 rulings, making his votes perhaps the most closely watched — and arguably most important — on the high court. Legal experts predict Kennedy will provide key votes on decisions that could strike down certain campaign contribution limits for individuals, weaken the influence of organized labor and curtail state-level affirmative action programs.

"He is the pivotal factor in many more 5-4 decisions than anyone else," said Jamie Raskin, a constitutional law professor at American University. "But just because you're the swing vote doesn't mean you're unpredictable. Often times he swings in perfectly predictable ways."

In June, Kennedy became a hero among gay rights activists when he sided with the 5-4 majority to throw out the federal Defense of Marriage Act. The ruling prohibits the federal government from denying benefits to same-sex couples who are legally married in states that recognize same-sex marriages.

Kennedy says he considers changing public opinions — particularly those involving gay rights — when making his rulings.

"It’s simply stunning to me to see the changes in attitudes” regarding sexual orientation, Kennedy said this month at the University of Pennsylvania. “It’s something I didn’t think about or know about as a kid. … But the nature of injustice is, you can’t see it in your own time.”

The same week as the DOMA decision, Kennedy voted with the majority in the 5-4 decision to strike down a key provision in the 1965 Voting Rights Act, a move that frees states of certain federal oversight of elections. His decision was applauded by conservatives, who viewed the provision as an encroachment on states' rights.

"He has not been a lockstep justice like [Clarence] Thomas or [Samuel] Alito, but he's still been a pretty faithful member of the conservative block on the court," Raskin said. "He's been with the conservatives on most important issues outside of gay rights and some civil liberty issues."

And while both sides of the political spectrum complain about "activist judges," Kennedy has accused Congress and state governments of often pushing the tough decisions off to the high court.

"Any society that relies on nine unelected judges to resolve the most serious issues of the day is not a functioning democracy," he said during his appearance at Penn.