It was 50 years ago this summer that Steven Spielberg’s “Jaws” terrorized moviegoers and became an instant classic.

Filmed on Martha’s Vineyard and adapted from Peter Benchley’s bestseller about a man-eating shark targeting the (fictional) Amity Island beach, “Jaws” charts how police chief Martin Brody (Roy Scheider), marine biologist Matt Hooper (Richard Dreyfuss) and grizzled shark hunter Quint (Robert Shaw) risk all to destroy the relentless predator.

Christopher Shaw Myers’ biography arrives today to celebrate “Jaws” with his family-focused memoir, “Robert Shaw: An Actor’s Life on the Set of JAWS and Beyond” (Citadel Press).

“The timing was just luck,” Myers said in a phone interview. “I never thought about writing a book about my Uncle Robert, who was my mother’s best friend, She was his older sister and she’s still here now at 95. I asked her before writing about her life, Robert Shaw and the whole family — for better or worse.”

The hard-living, hard-drinking Shaw’s heart gave out. He was 51 when he died in 1978.“The last time I spent time with him was when I was 18, just before ‘Jaws’ came out.

“Robert came to appear on ‘The Mike Douglas Show’ which filmed in Philadelphia. He arranged a private screening for the family and took us to lunch where he was telling behind the scenes stories, mostly about how his mother had embarrassed him in front of Richard Dreyfuss, Steven Spielberg and Roy Scheider.”

Myers believes that starry acting trio is one reason “Jaws” still rates. “Those characters point back to Plato’s ‘Republic’ where he described people and society as three categories.

“You’ve got Shaw’s Warrior, Dreyfuss’s nerdy Intellectual, and then the Statesman, Scheider’s police chief who is trying to weigh both sides. These are classic characters who embody so much of what we see in the world.

“The other thing is Quint’s USS Indianapolis speech” — where he recalls the sharks feasting on the helpless crew of their capsized ship.

“I can’t think of many movies that have a speech like that. It’s near the end of the movie and up to that point Quint has made no sense. He has sabotaged them from the moment they left the dock. Just inviting trouble.

“You don’t understand him until he says, ‘Hey, look! This is what happened to me.’ And suddenly you feel sympathy for him.

“To me — and this may be overstating things — it’s similar to the Shakespearean soliloquy in ‘Hamlet.’ You know, ‘To be or not to be.’ Should I kill myself?

“What Quint does in that film is raise it to another level — and that’s why I think people continue to watch it every year.”