The great tenor Enrico Caruso sang about 60 roles; the storied diva Maria Callas, roughly 50. Renée Fleming, the most famous soprano today, says she has sung about 55.

But Plácido Domingo has blazed past them all. And on Thursday, when he takes the stage for a concert performance of Bizet’s “The Pearl Fishers” at the Salzburg Festival in Austria, Mr. Domingo will reach a virtually unheard-of milestone in opera history: He will sing his 150th role.

“If you look at the history of singers in opera, he stands by himself,” Joseph Volpe, the former general manager of the Metropolitan Opera, said. “If there was ever a giant in any industry, it’s Plácido Domingo. He’s unmatched.”

Now 77, well past the age at which most star singers retire, Mr. Domingo has performed nearly 4,000 times in a six-decade career, recorded more than 100 albums, and become a household name as one of the Three Tenors and in appearances on “Sesame Street” and “The Simpsons.” And he has continued to add voraciously to his repertory, choosing roles to match his changing voice, while also becoming a prominent conductor and arts administrator. It’s as if Tom Brady were still winning Super Bowls in his 50s — while playing three sports at once.