You can’t get to sleep. You’re tossing and turning. You want someone to read you a nice, wholesome bedtime story. And you want that someone to be the actor Jimmy Stewart.

The sleep and meditation app Calm on Tuesday released a new story for premium users told by Mr. Stewart, the beloved actor who starred in “It’s a Wonderful Life.” But the voice in their ear lulling them to sleep is not from Mr. Stewart, who died in 1997. It is a version of his signature drawl generated by artificial intelligence.

“Well, hello. I’m James Stewart, but, well, you can call me Jimmy. Tonight I’m going to tell you a story,” the clone of Mr. Stewart’s voice begins, telling listeners to make themselves “nice and comfortable.”

“It’s a heartwarming story of love, of loss, of hope and of joy,” the voice continues. “But most of all, it’s a wonderful sleep story.”

The app is known for its “Sleep Stories” — tales read by celebrities including Idris Elba, Matthew McConaughey and Harry Styles to help users drift off to sleep. But for its Stewart story, it enlisted the help of Respeecher, a company based in Ukraine that uses A.I. technology to produce synthetic speech and clone voices.

The story, written by Calm’s creative team, is the first of its celebrity narrations to use an A.I.-generated voice, a spokeswoman for the app said on Tuesday, adding that the company collaborated closely with the actor’s estate on the project. “Stewart is one of the most beloved actors in history, with a voice that is heartwarming to many,” the spokeswoman said in an email.

Respeecher said that CMG Worldwide, the company that manages Mr. Stewart’s licensing, approved the project. CMG said in a statement: “The ability to replicate and integrate the unique voices of artists into contemporary works introduces a dynamic fusion of tradition and innovation.”

Similar projects might be on the way, the company added, saying it wanted to “bring many of the icons that we represent to a whole new generation of admirers,” according to Tina Xavie, its chief marketing officer.

“This technology not only allows for the continuation of the artistic contributions of those who have passed away but also provides living artists with new and groundbreaking avenues for expression,” the statement said.

To revive Mr. Stewart’s voice, Respeecher fed recordings of the actor into its system to train it to recognize the voice. It then combined it with that of a voice actor who read the new story, said Alex Serdiuk, chief executive and co-founder of Respeecher, in a video interview from Kyiv.

“The voice is iconic. It’s very recognizable, he said, adding that it tied in well with Christmas. “It’s just a cool story and it contributes a lot to mental health awareness.”

The increased use of A.I. to recreate the likenesses or voices of public figures in film, television and other content has become a contentious issue. Meta, for example, has introduced A.I.-powered characters based on celebrities like the rapper Snoop Dogg and the former N.F.L. quarterback Tom Brady that it will soon weave through its products.

Critics have raised questions over the ethics and regulation of the practice. The use of A.I. by studios and entertainment companies was among the concerns at the center of strikes this year by Hollywood writers and actors.

Recently, the actor Tom Hanks and the news anchor Gayle King warned their followers on social media that their likenesses had been used in unauthorized advertisements. Cybersecurity experts have also cautioned that technology like “voice deep fakes” could help scammers steal from people or businesses or commit other crimes.

Mr. Stewart’s family consented to the Calm project, according to Variety, which earlier reported the story.

Respeecher, founded in 2018, has synthesized voices for 150 projects, including the football coach Vince Lombardi for a video at a Super Bowl. It is currently working with Warner Music France, it said, on an “animated biopic” of the French artist Edith Piaf, who died in 1963, that will use A.I. to generate her likeness and voice. Its technology can also produce voice overs for media that would otherwise be laborious for actors to record, or convert recordings to other languages using the original actor’s voice.

The company has said that it does not allow its technology to be used for “deceptive uses,” including uses that would impinge on a subject’s privacy and ability to find work.

“In practice, this means we will never use the voice of a private person or an actor without permission,” the site says, but adds that the company would allow “nondeceptive uses” of historical figures and politicians.

Mr. Serdiuk said the company was aware of the concerns around the voice technology. They had introduced it with ethics policies that have only become stricter, he said, around gaining consent to use any intellectual property. “We are not letting anyone using our technology or tools to introduce a voice that they have no rights to,” he said.

He added that he was planning to listen to the Jimmy Stewart story later that night before bed.