As a little boy, Frank Welker was blessed with the “strange, innate ability” to mimic the sound and speech of animals. Jockeying for attention at the family breakfast table, he would offer up dead-on impressions of the sparrows chirping on the front lawn.

“I was the youngest in the family,” Welker said. “I found that by acting peculiar I could get my piece of the attention.”

He got it all right, and spun it into career gold. A successful voice actor since the 1960s, Welker has cornered the market on all creatures great and small. Now, at 74, he has one of his first “starring” roles in a major motion picture — as the voice of Scooby-Doo in the animated “Scoob,” which arrives Friday via video-on-demand.

An invisible but indispensable presence, Welker has more credits (roughly 850) than any movie star, and a cumulative box office that puts them all to shame. He’s played gremlins in “Gremlins”; Spike the dinosaur in “The Land Before Time”; Max the dog in “The Little Mermaid”; a sentient footstool in “Beauty and the Beast”; Santa’s Little Helper in “The Simpsons”; and — in “Aladdin” alone — Abu the monkey, Rajah the tiger and the growling Cave of Wonders.

He portrayed “the biggest thing in the movie and, in some ways, the smallest thing in the movie,” said “Aladdin” co-director John Musker, “and both equally compelling. That’s what Frank could do.”

If it roars, squawks, barks or screams, Welker’s your guy. He’s known as “the king” and “the godfather” among his fellow voice actors, said Tress MacNeille, the voice of characters such as Babs Bunny in “Tiny Toon Adventures” and Agnes Skinner on “The Simpsons.”

“He was the sophomore in college when we were the freshmen in high school,” said MacNeille, who has been working with Welker since 1981. “I always made sure that I sat right next to Frank in the studio. You could just learn vocal tricks and stylization tricks, and of course you would listen to his impressions and that would inform your own. He was a great teacher.”

When the casting director for “Futurama” was looking for someone to voice Nibbler, an adorably ravenous, three-eyed alien, MacNeille piped up: “Oh, that’s Frank’s job.”

“That’s kind of an expression that we use,” she said, “when there’s something that’s thrown at us and we can’t do it — a sound effect or a certain impression or something really special — we say, ‘Oh, that’s Frank’s job.’ ”

Maybe that’s because “nobody else wanted to do it,” Welker laughed. “A lot of it was pretty painful, and I had like a military-grade voice, you know — a leather throat.”

Welker grew up in Denver, the son of an electromechanical engineer and a secretary who were both “salt of the earth, hard-working” people, he said. “My dad was pretty much a genius, so I don’t know what happened to me. I think I was dropped on the floor early.”

He leveraged his uncanny gift for vocal imitation — including of celebrities, but mostly critters — to impress family and school friends, and eventually an audience.

After moving to California in 1966, where he dove headlong into the theater department at Santa Monica College, he acted in stage adaptations of fairy tales (alongside future animation tycoon Don Bluth), got an agent and landed a detergent commercial. He hasn’t stopped working since.

Initially, Welker divided his pursuits between onstage comedy and on-camera roles — he shared the screen with Elvis Presley in “The Trouble With Girls” and starred with Richard Dreyfuss in an unsold pilot based on “Catch-22.” He gave up the notion of being a serious actor quickly, though, after his audition for a TV western — a death scene — drew giggling laughter.

In comedy clubs, he was billed as an “impressionist” and even a “verbal clown,” his act involving a menagerie of dogs, cats and geese, climaxing with an entire chorus of ducks singing “We Wish You a Merry Christmas.”

“I had like 20 minutes of questionable comedy — not in the dirty sense,” he said, “but just in whether it was funny or not.”

At the Los Angeles club Ledbetter’s, Welker performed on opposite nights from a young Steve Martin. He toured around the country with singer Glen Campbell as the opening act for the Righteous Brothers — and actually performed at the Cocoanut Grove, the famous L.A. nightclub inside the Ambassador Hotel, on the night Robert F. Kennedy was assassinated in the hotel’s kitchen.

He was already at home in bed when it happened, but said he’ll never forget that day “because I actually had to go right through part of the kitchen to get to the Cocoanut Grove.” His set included an impression of the Kennedys.

It seems Welker was destined for a unique life of fame adjacency — unseen but ubiquitous.

Part of his voice-over career has been dubbing lines for famous actors. His first big gig was providing Rex Harrison’s animal communication in the original “Doctor Dolittle.” He screamed the screams for a rapidly aging Spock (Leonard Nimoy) in “Star Trek III: The Search for Spock” and subbed in for George C. Scott singing “Home on the Range” in “The Rescuers Down Under.”

In the hall of fame of famous animals, he’s played Smokey Bear, Garfield, Kermit the Frog and Woody’s horse, Bullseye, in the “Toy Story” movies. Besides Abu, he also voiced the capuchin monkey who croaks from a “bad date” in “Raiders of the Lost Ark” — oh, and he’s Curious George.

Welker is an animator’s muse, Musker said, not just because he’s a “man of a thousand voices” or such a talented zoological mimic.

“There’s a scene where Abu really mocks Aladdin because he’s sweet on Jasmine,” the director said. “He does a little sashay, where he’s like ‘Ooh yeah, pretty girl, huh?’ Frank came up with a way of doing that where he totally got the attitude, even though there wasn’t a word of dialogue.”

And it all started in 1969, when Welker’s barnyard of voices landed him a dog food commercial, which got him into an audition for a new Hanna-Barbera show about a food-crazed dog named Scooby-Doo. Welker was eventually cast — but as the teenage straight man Fred Jones.

Starting out with the legendary voice actor Don Messick as Scooby and Casey Kasem as Shaggy, Welker has been a key member of Mystery, Inc. for more than 50 years. After Messick died in 1997, Welker eventually took over the iconic role of the talking, charming, often petrified canine who puts R’s in front of every word.

Even though the cast of “Scooby-Doo” all had fun doing impressions of one another, Welker was initially uncomfortable with stepping into his friend’s shoes. But he took up the mantle in 2002, thinking “maybe that could feel as though I could do a tribute to Don — and the fans. We were all part of this same family, the Scooby family.” (“Scoob” pays homage itself by setting some of the film’s action on “Messick Mountain.”)

So is it a blessing, after decades of work and hundreds of parts, to have an inescapable voice and yet an inconspicuous face?

“My ego says no,” he wrote, “but my reality says yes.”