NEW YORK -- When he plays King Lear, Sam Waterston doesn't worry about being influenced by any other actor.

"I've never seen 'Lear.' I haven't ever," the actor says before a recent performance at the Public Theater.

That's a somewhat remarkable admission for an actor who adores Shakespeare and has played many of the Bard's roles, including Hamlet, Polonius, Laertes, Prospero, Leonato, Prince Hal, Silvius, Cloten and Benedict.

Waterston, who turns 71 this month, has been itching to play Shakespeare's crazed dictator since he did Hamlet three decades ago. "I thought, 'Well, you've got to get old, there's no way to avoid that, but at least there's Lear to look forward to.'"

The seven-time Emmy nominee is clearly jazzed about the role, one of Shakespeare's meatiest. "This is big," says Waterston, whose salt-and-pepper hair is now long but whose eyebrows remain bushy. "This is idiotic to be saying this, but it's a great, great play."

Waterston, from 1994-2010, played prosecutor Jack McCoy on "Law & Order" and has been a reassuring image on TV commercials.

The fact that his Lear will be at the Public (it runs through Nov. 20) is fitting since Waterston credits it with launching his career. "They brought me to public attention and then they've given me the opportunity to do so many great parts."

Born in Cambridge, Mass., to parents who were teachers and amateur actors, Waterston graduated from Yale University, where he majored in drama, and attended the Sorbonne in Paris.

Waterston's acting breakthrough came in 1972, playing Benedict in the Public's New York Shakespeare Festival production of "Much Ado About Nothing." The show was such a big hit that it was filmed for broadcast on CBS.

That led to Waterston playing Nick Carraway in "The Great Gatsby" opposite Robert Redford and the role of Tom Wingfield in a TV production of Tennessee Williams' "The Glass Menagerie," starring Katharine Hepburn, for which he got his first Emmy nod.