HE’S long and lean — a human string bean in a stringy blond wig. He stumbles and falls, and when he speaks, his voice rises up, valley girl-style, like an unanswered question.

He’s Hamish Linklater, and his Sir Andrew Aguecheek, the knuckle-headed knight of the Public Theater’s “Twelfth Night,” is so hilarious, you can’t take your eyes off him.

Then again, he’s been living with the Bard all his life: His mother helped found the Berkshires, Mass., troupe, Shakespeare and Company, when he was 2.

“They did Shakespeare on the hill, and I’d be in a sleeping bag,” the 32-year-old says.

“All the company members started to reproduce at a certain point, and the director would shove us in as fairies and elves — little kids in tighty-whities and togas.”

Kristin Linklater — who’s tutored Patrick Stewart, Donald Sutherland, Mary Tyler Moore, among others — recalls the first time her son got Shakespearean.

“When he was 4 or 5, there was a bunch of us chattering away, and he was on the rocking horse, going, ‘To be or to not to be, to be or to not to be . . .

“He was always good at it.”

But while he’s since played Hamlet twice — with the correct phrasing — most people probably know Linklater best as Julia Louis-Dreyfus’ brother, the manny, on TV’s “The New Adventures of Old Christine.” He’s done a few movies, too — “Fantastic Four” among them.

Indeed, his heart these days is in Los Angeles, where he lives with his wife and their 2-year-old daughter.

Getting him back to the Delacorte — where he played Laertes 10 years ago — took some pictures and a line.

“Dan [Sullivan] sent me a picture of the set when he offered me the part,” he says, “and I thought, I don’t know who this character is, but I think he’ll run and fall down a lot of hills.”

And that he does — Linklater has the nicks and bruises to prove it.

What really sold him, he says, was the writing. “Sir Andrew has this beautiful line, ‘I was adored once, too,’ ” Linklater says.

“You’d fly 3,000 miles and bring your family with you just to say that line, in the open air.”