There is no shortage of ancient proverbs, some still in popular use, that describe what happens when women get close to power. “A great beauty will bring about the downfall of cities and nations,” goes one of them.

More recently, such sentiments were reinforced by Jiang Qing, the former actress and third wife of Mao, who was saddled with much of the blame for the Cultural Revolution and received a commuted death sentence. The fact that she was in show business before she turned rabid revolutionary has probably not helped Ms. Peng.

She appears to have followed a set of unwritten rules about the comportment of women attached to important men. The higher her husband climbed the Communist Party ladder, the less visible she became. She once told a Singapore publication that she performed as many as 350 concerts a year in the 1990s, including one at Lincoln Center in New York. But these days she no longer accepts paid appearances “for the sake of the party.” Since her husband’s ascension to the Politburo Standing Committee in 2007 she has all but disappeared from the annual Spring Festival gala.

Ms. Peng, who was born in a small town in the northeastern province of Shandong and joined the army at age 18, found fame long before she met Mr. Xi. When the couple was introduced by a mutual friend in 1986, she was already known as “the peony fairy” and the “outstanding songbird of the century.”

MR. XI, the son of a revolutionary hero, was a midlevel official in Fujian Province, newly divorced from his first wife. Ms. Peng, who turns 50 on Tuesday, is nearly a decade younger than Mr. Xi. In an interview she gave to Zhanjiang Evening News in 2007, she said she was unimpressed with him at first glance. “Not only did he look rustic, but he also looked older than his years,” she said. But once Mr. Xi opened his mouth, her objections faded. They married a year later.

Their relationship has required many compromises. The two are seldom together, she said, and in 1992, his official duties during a typhoon in Fujian forced him to miss the birth of the couple’s daughter, now a student at Harvard University. Even being in the same city does not guarantee face time. “People would gossip if I bring my wife with me all the time,” he reportedly told her. “It’s not good for our images.”

Her public image has gone through a makeover since Mr. Xi was set on the path to becoming party secretary, even losing her voluminous gowns for matronly pantsuits or crisp military uniforms. The censors have also clipped her wings, removing all but the most anodyne information about her from the Web and blocking her name on China’s version of Twitter.