Duff, 19, and Madden, 27, filed requests in Superior Court on Thursday for protection from David Joseph Klein, 50, and a man identified by first name as Max, according to court papers.
The documents claim that Max "Doe" is a 19-year-old Russian immigrant who came to Los Angeles for "the sole purpose of meeting and becoming romantically involved" with Duff, a multi-platinum recording artist and former star of TV's "Lizzie McGuire."
"He has admitted to being 'obsessed' with her, has stated his intention of removing his 'enemies' (i.e. those who prevent him from being with her), has stated his intention of purchasing a weapon, and has threatened to kill himself and to engage in dramatic actions to get her attention," the court documents claim.
Klein and Max could not be reached for comment; there was no phone listing for Klein.
According to the papers, Max rooms with Klein, who says he is a celebrity photographer.
"Over the past six weeks, the defendants have engaged in an accelerated effort" to contact Duff, including visits to her neighborhood, her mother's home, Madden's neighborhood, a venue in Hollywood where Madden and Good Charlotte performed, and direct calls to Duff's manger, the documents claim.
Los Angeles police detained Max outside of Good Charlotte's concert after the band's security personnel alerted authorities to the pair's presence, according to the papers.
Duff and Madden are requesting that Max and Klein stay at least 100 yards away from them, Duff's sister Haylie, 21, her mother Susan, 53, and Madden's twin brother Benji.
Duff's publicist Ivy Mullencamp and the couple's attorney Larry Stein declined to comment.