Stan Lee is suing the entertainment company he co-founded for $1bn (£742m).
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 bosses surreptitiously made Lee sign away his name and image rights in the deal.
POW! are yet to respond but previously expressed “concern” over his wellbeing.
The BBC has contacted POW! and the Hong-Kong based Camsing International Holding, who owns it, for comment.
Lee, the co-creative force behind many superhero characters, including Black Panther and Spider-Man, sold the company to Camsing last year.
But the suit alleges POW! CEO 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.
It says Lee was “in a state of total devastation” and that Champion and Duffy were “opportunists” who “saw a chance to take advantage of Lee’s despondent state of mind”.
Plea for help
“In addition, POW! took control of Lee’s personal social media accounts, including Facebook, Instagram and Twitter, thereby impersonating Lee before a combined 15 million followers worldwide,” the complaint reads.
Lee appeared to regain control of his Twitter account on Tuesday night and used the platform to confirm to fans that 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.