The lawsuit claims that Bruce DiMattia was "overcome by greed" and was "jealous of his former friend's success," so he threatened to disclose personal information about the actor unless Willis bought him a car and paid him at least $100,000.
DiMattia worked for Willis — and lived rent-free in a house owned by the actor — from 2002 until 2006, the lawsuit said.
He was responsible for maintaining Willis' personal items and memorabilia and organizing photographs and videos of the actor and his family.
DiMattia's employment ended this year, but he has refused to move out of the house and still has Willis' private photos and other property, according to the suit.
Willis is seeking at least $1 million in damages, according to the suit filed Aug. 1.
Willis' attorney, Martin Singer, said the suit was served to DiMattia "within a day or two of being filed," adding that the case would likely go to trial in a year.
DiMattia has not yet named a defense attorney, according to a court clerk. There was no telephone listing for him in the Los Angeles area.