Sci-fi screenwriter Bryant Moore claims the legendary filmmaker based Avatar on his scripts for two projects called Aquatica and Descendants: The Pollination, adding that there are too many plot similarities between his ideas and Cameron's movie for them not to be linked.
Moore is also taking action against Cameron's production company Lightstorm Entertainment, and executives at movie studio 20th Century Fox and is demanding the huge sum for damages, reports TMZ.com.
Avatar raked in £1.7 bn worldwide to become the highest-grossing film of all time.
It's the second such lawsuit Cameron is facing - another plaintiff, Eric Ryder, filed copyright infringement papers against the star earlier this month, alleging he had approached Lightstorm bosses with an idea for an "environmentally themed 3D epic" in 1999 - a decade before Avatar was released.
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