Writing tool Grammarly has disabled an AI feature which mimicked personas of prominent writers, including Stephen King and scientist Carl Sagan, following a backlash from people impersonated.

The Expert Review function, which offered writing feedback "inspired by" the styles of famous authors and academics, was taken down this week by Superhuman, the tech firm which runs Grammarly.

The feature was met with resistance, including a multi-million dollar lawsuit, from writers who found their names and reputations used as "AI personas" without their consent.

Shishir Mehrotra, the firm's chief executive, apologised on LinkedIn, acknowledging the tool had "misrepresented" the voices of experts.

Investigative journalist Julia Angwin, a New York Times contributing opinion writer, is the lead plaintiff in a class-action lawsuit filed against Superhuman and Grammarly in the Southern District of New York.

Angwin told the BBC she was "stunned" to find her professional identity being marketed as a commercial product.

"I had thought of deepfakes as something that happens to celebrities, mostly around images," she said.

"Editing is a skill... it's my livelihood, but it's not something I've ever thought about anyone trying to steal from me before. I didn't even think it was stealable."

The legal filing alleges that the tech firm misappropriated the identities of "hundreds" of writers to drive profits for its paid subscription service.

According to Angwin's lawyer, Peter Romer-Friedman, the case has already seen significant momentum.

"We've heard from over 40 people in the last 24 hours since we filed the suit," he said, describing the company's actions as a "brazen violation of the law."

The lawsuit argues it is unlawful to use names for commercial purposes without consent and seeks to stop the platform from attributing advice to experts that they "never gave."

While the filing states that damages exceed $5m (£3.7m), Romer-Friedman noted that this is a minimum jurisdictional requirement and the true figure will be calculated based on the firm's earnings from the tool.

For Angwin, the quality of the AI's output added insult to injury, describing the imitation as a "slopperganger" - a reference to content described on social media as "AI slop".

"The edits were not good. The ones that they were attributing to me... were making the sentences worse, more complex," she said.

"The idea that my name would be in there giving people terrible advice is actually really appalling."

Grammarly was founded in 2009 as a writing-review tool and began integrating a suite of generative-AI tools in August 2025.

Part of this was the Expert Review function which appears to have launched without the named famous personas introduced later.

Although the company began rebranding to Superhuman in October, Grammarly was kept as the name of its main service.

As criticism mounted in recent days, Superhuman initially said it would maintain the feature but allow those named to "opt-out", according to The Verge.

Wes Fenlon, a gaming journalist whose persona was used in the tool, wrote on BlueSky: "Opt-out via email is a laughably inadequate recourse for selling a product that verges on impersonation and profits on unearned credibility."

Romer-Friedman argued that the burden of consent should never have been on the writers.

Mehrotra said in response to the backlash: "Over the past week, we received valid critical feedback from experts who are concerned that the agent misrepresented their voices.

"This kind of scrutiny improves our products, and we take it seriously."

He said the AI agent had drawn on "publicly available information from third-party LLMs to surface writing suggestions inspired by the published work of influential voices".

The firm's chief executive apologised, adding: "We hear the feedback and recognize we fell short on this."

Responding to the lawsuit, Mehrotra told the BBC: "We announced that Expert Review was being taken down for a redesign before the claim was filed, and in its short lifespan it had very little usage.

"We are sorry, and we will rethink our approach going forward."

However, he said the legal claims within the lawsuit are "without merit" and the company will "strongly defend against them".

He added the firm is working on a "better approach to bringing experts onto our platform" in a way that will "benefit both users and experts".