Stan Lee is suing the entertainment company he co-founded for $1bn (£742m), according to legal documents.
The comic book legend alleges he was coerced into a fraudulent sales agreement when he was in an emotionally and physically fragile state.
The complaint, filed in LA on Tuesday, claims Pow! Entertainment made Lee sign over his name and image rights.
Pow!’s parent company Camsing International Holding said it was “not aware” of legal documents being served.
The Hong Kong-based company, which bought Pow! in 2017, said it is currently “seeking legal advice” on the basis of media reports about potential litigation and “may take legal action if appropriate”.
Pow! Entertainment is yet to respond directly, but has previously expressed “concern” over Lee’s wellbeing.
Lee is the co-creative force behind many superhero characters, including Black Panther and Spider-Man.
The lawsuit alleges Pow! chief executive Shane Duffy and co-founder Gill Champion “conspired and agreed to broker a sham deal to sell Pow! to a company in China and fraudulently steal Stan Lee’s identity, name, image, and likeness as part of a nefarious scheme to benefit financially at Lee’s expense”.
The complaint, lodged at Los Angeles County Superior Court, states Lee does not recall signing sale documents, nor having them read to him.
The suit draws attention to the death of Lee’s wife last July, and his degenerative eye condition which has caused his poor eyesight, suggesting he could not have read the documents.
The legal papers also say Pow! took control of Lee’s personal social media accounts. He appeared to regain control of his Twitter account on Tuesday and used the platform to tell fans his social media channels had been “hijacked”.
“From now on, I will depend on you, my dear fans, to protect and defend me,” he added.
The comic book writer went on to post his first Twitter video – with the help of fans – to express further gratitude.
“I just want to tell you I love your comments on Twitter – I don’t know how much I have been missing now that I see them,” he said.
“I appreciate everything you say and do, I love you all – let’s keep up the great relationship”.
The nonagenarian signed off with his signature phrase “excelsior!” – implying triumph.