But his path to singing Siegfried at the Met — he also sings in “Siegfried,” the third “Ring” opera, on May 2 and another “Götterdämmerung” on May 4 — was unusual. Mr. Schager, who was born Andreas Schagerl in the small town of Rohrbach an der Gölsen, started his career in operetta (precursors to modern musical comedies) and lighter tenor roles.

“Austrian tenors are always going for operetta,” he said. “For 12 or 13 years, I sang works like ‘Der Zigeunerbaron’ sometimes twice a day — works that are totally different and unknown to people who listen to Wagner.”

When he took his first stab at Wagner in 2009 — as David, a relatively lyrical part in “Die Meistersinger von Nürnberg” — Mr. Schager dropped the final letter of his last name on the advice of a colleague.

“It’s difficult if you want to start an international career as a heldentenor with the name Andreas Schagerl,” he recalled the colleague telling him. “Because if you type it into Google, you only find operetta. Many opera directors will see this and won’t even invite you to audition.”

But little else about his vocal transition was calculated. Asked about how the change came about, Mr. Schager replied matter-of-factly: “It happens.”