“Telling the truth is no longer the benchmark for public service,” he said. “It’s no longer the salve to our fears, or the guide to our actions. Truth is now considered malleable, by opinion and by zero sum endgames.”

That left the more than 9,000 graduates at Harvard’s 372nd commencement with a choice to make, said the Hollywood icon, who has played an astronaut, a soldier, a little boy in a man’s body and even a Harvard professor in a decades-long movie career.

“It’s the same option for all grownups who have to decide to be one of three types of Americans: Those who embrace liberty and freedom for all; those who won’t; or those who are indifferent,” he said. “Only the first do the work of creating a more perfect union, a nation indivisible. The others get in the way.”

Near the end of the speech, he drove the point home to a group that included not just undergraduates but those who graduated from Harvard’s professional and extension schools.

“The responsibility is yours. Ours. The effort is optional. But the truth, the truth is sacred. Unalterable. Chiseled into the stone and the foundation of our republic,” he said.

Hanks, who was awarded an honorary doctor of arts degree, poked fun at his own lack of academic credentials on a stage filled with some of the world’s brightest minds and most accomplished scientists.

“It’s not fair, but please don’t be embittered by this fact,” Hanks said. “Now, without having done a lick of work, without having spent any time in class, without once walking into that library — in order to have anything to do with the graduating class of Harvard, its faculty, or its distinguished alumni — I make a damn good living playing someone who did,” he said in reference to his depiction of fictional Harvard professor Robert Langdon in three movies based on Dan Brown’s novels — “The Da Vinci Code,” “Angels & Demons” and “Inferno.”

“It’s the way of the world, kids,” he said to a chorus of laughter.

Before Hanks headed to the podium to give his speech, Harvard President Lawrence Bacow, presiding over his last commencement before stepping down, called Hanks, “Wilson’s bestie, Buzz’s buddy, Ryan’s savior, America’s dad,” and presented him with a Harvard volleyball, in tribute to his role in “Cast Away,” where to stay sane his character talks to an old volleyball.

Hanks proved to be the most popular person on stage, posing for selfies with faculty members before the ceremony and giving congratulatory fist bumps to dozens of Harvard students who graduated summa cum laude.

“May goodness and mercy follow you all the days,” he said, referencing a biblical verse. “All the days of your lives. Godspeed.”