Perhaps it was Bob Hope who showed Caroll Spinney just how universal the appeal of Big Bird is. Spinney has performed as the Muppet character since the debut of “Sesame Street,” in 1969. He’s Oscar the Grouch, too.

Spinney, 81, is the subject of a new documentary, “I Am Big Bird,” which opens at the Brattle Theatre on Friday.

The original idea had been to have another Muppet, Kermit the Frog, appear on “Bob Hope’s World of Comedy,” a 1976 NBC television special. Kermit (Jim Henson) was unavailable. So Big Bird (Spinney) substituted.

Hope, unfamiliar with the character, was politely unenthused. That changed at the first rehearsal. Spinney, in costume, looked at Hope and ad-libbed in that unmistakable sweet-tempered voice, “Boy, I thought had a big beak.” The comedian collapsed with laughter. “That’s one of the great satisfactions of my life,” Spinney says.

He’s sitting in the living room of his house, which he designed, in this small town near Sturbridge. The house is modeled on an Austrian chalet. The grounds include a pond, acres of woods, and seven other buildings. One of them is a toy shop, which Spinney and his wife, Debra, occasionally open up for local children. They’re toys they’ve gathered over the years in their travels, which have been extensive. Big Bird may not fly, but in that sense, he’s certainly migratory. Spinney has three children of his own, from his first marriage.

Next month the Spinneys celebrate their 42d anniversary. The couple divide their time between here and a studio apartment on the Upper West Side of Manhattan. With luck, the drive to New York for “Sesame Street” tapings takes two hours and 40 minutes.

Spinney’s voice is pleasantly reedy, perched midway between Big Bird’s high-pitched sunniness and the low tones of Oscar’s growl. He has the snowy hair and kindly manner of an ideal uncle — yet with enough of a twinkle in his eye to show that this particular uncle retains a nephew’s high spirits. How high? One of the more memorable moments in “I Am Big Bird” is video footage of Spinney, in his 60s, bungee-jumping in New Zealand.

Chad N. Walker, who co-directed the documentary with Dave LaMattina, recently talked about Spinney in a telephone interview. “Very rarely do you meet somebody, and they’re exactly how you’d hope they’d be,” Walker says. “It was such a delight to work with Caroll because he was exactly the way you’d want Big Bird to be.”

“I can’t imagine walking away from being Big Bird,” said Caroll Spinney. “I still get in the suit, but not every day. Which is wonderful, because I want to do 50 years, and more than the 50 if I can.”

That the character is the way he is owes a lot to Spinney. Jim Henson’s original conception of Big Bird had been as a feathered version of Walt Disney’s Goofy or Edgar Bergen’s Mortimer Snerd: sweet and lovable but also a bit dim. Spinney saw things differently from inside the yellow costume. Rather than a “yokel,” he says, Big Bird “should be a kid. He’s learning, like the kids watching at home. He doesn’t know the alphabet yet, for instance.” And that’s who the bird became: someone for young viewers to relate to rather than just laugh at.

Born in Waltham, Spinney grew up there and in Acton. “When I was a child I didn’t know if I was going to be a puppeteer or a cartoonist,” he says. “But I knew it was going to be one or the other.”

It turned out to be both. When not performing, Spinney frequently sketches and paints. He proudly shows off albums filled with his renderings of Big Bird and Oscar. But it’s as a puppeteer and performer that he’s earned his living. After a stint in the Air Force, Spinney moved to Brookline and spent nine years working on the Bozo the Clown show, on Channel 5.

“I had an awful lot of fun doing the show,” Spinney recalls. He speaks fondly of Frank Avruch, who played Bozo, and notes with a laugh that during the first few years of “Sesame” “Bozo” paid better. In fact, Spinney went back to “Bozo” during the four-month break between the first and second seasons of “Sesame Street.”

That was 46 years ago. In the years since, Spinney has had a remarkable range of experiences.

“I’ve sung at Carnegie Hall. I danced with Cynthia Gregory, the ballerina. I’ve performed with Isaac Stern — he even let me touch his Stradivarius.”

Spinney (or Big Bird) has held hands with Henry Fonda, performed in front of every first lady since Pat Nixon, and conducted symphony orchestras. Kathleen Turner popped into his dressing room unannounced. A 17-year-old Michael Jackson expressed mystification at how Spinney dealt with Oscar’s living arrangements. “How do you fit into that little trash can? You’re so big, and it’s so small.”

Spinney now splits Big Bird duties with his understudy, Matt Vogel. “I was, of course, amused and delighted when I found his name is Vogel” — “bird,” in German. “I can’t imagine walking away from being Big Bird,” Spinney says, and cutting back helps ensure he can keep on. Although he looks years younger than his age, he is in his 80s, after all. “I still get in the suit,” Spinney says, “but not every day. Which is wonderful, because I want to do 50 years, and more than the 50 if I can.”

For as long as there’s been a Big Bird, Big Bird has been Spinney. But Caroll Spinney wasn’t always Caroll Spinney.

“My mother spelled it ‘Carol,’ ” Spinney explains. “That’s Latin for ‘Charles.’ It was so often mistaken for a woman’s name, I added another ‘r’ and another ‘l.’ After I met Deb, I decided to take out one ‘r,’ to make it unusual.” He shrugs and smiles. “It doesn’t really matter. I know who I am.”