STORY: Shares of GameStop more than doubled Monday morning after the return of "Roaring Kitty" - a former marketer at an insurance firm credited with sparking the meme stock rally of 2021.

Keith Gill posted on X-dot-com after a three-year absence.

He was a key figure in the in the so-called Reddit rally, which saw shares of GameStop surge as much as 21-fold over two weeks in January 2021 before crashing to pre-surge levels in the subsequent days.

Its rally spread to other highly shorted stocks and drew scrutiny from U.S. regulators.

Gill's post on Sunday was a sketch of a man leaning forward in a chair, a popular meme among gamers that indicates things are getting serious.

He did not immediately respond to a Reuters request for acomment.

GameStop's shares hit a one-year high on Monday and were halted multiple times for volatility.

The stock was trending on investor-focused social media stocktwits.com, indicating interest from individual investors.

Roaring Kitty and retail trading platform Robinhood were trending on X.com.

The videogame retailer in March cut an unspecified number of jobs to reduce costs and reported lower fourth-quarter revenue.

The company has about a quarter of its publicly available shares in short position and the bearish investors were set to lose $437 million on paper on Monday, analytics firm Ortex said.