Quitting while ahead is never easy, but walking away while on top is truly rare. So it was startling to hear Marlis Petersen, the German soprano who reigns in the daunting title role of Berg’s “Lulu,” disclose this week that she plans to retire the part after she sings it in the eagerly anticipated new production by the artist William Kentridge that will have its premiere next week at the Metropolitan Opera.

After all, the current issue of Opera News describes Ms. Petersen as an interpreter of Lulu who has made the part “hers and almost hers alone,” adding that “only a few other sopranos have made a similar impact in the role.” The German magazine Opernwelt recently named her its singer of the year for her performance last spring in Munich as Lulu, an object of relentless desire who is cruelly used by a series of men, kills her husband, becomes a prostitute and is finally killed by Jack the Ripper. The new “Lulu” coming to the Met will be her 10th production of the opera — and, she said in an interview, her last.

“It’s good to stop on a good high point,” Ms. Petersen, 47, said on Monday afternoon after rehearsing the role onstage at the Met and changing out of her costume and makeup, which had helped transform her into a beguiling, vulnerable and, of course, tragic Lulu, who recalled the silent film star Louise Brooks with a dash of Marlene Dietrich.

“It’s been 18 years now, with 10 productions, and I have a feeling it’s time to put her to sleep,” said Ms. Petersen, an intense singing actor. “I’m sad about that. It’s not that I can’t do it anymore; it’s just that I think I need to — how can I put it? — it has sneaked so much into my system that it rules my life somehow, this part.”