Six years before he died, Himan Brown, the creator of the radio dramas “Dick Tracy” and “Inner Sanctum Mysteries,” signed papers ensuring the bulk of his $100 million estate would go to a charitable trust under the sole control of his longtime lawyer.

Now a lawsuit alleges that the lawyer, Richard L. Kay, duped Mr. Brown, who was 94 at the time, into leaving the radio-era fortune in Mr. Kay’s hands. The court papers assert Mr. Kay has exploited his position overseeing the trust for his own benefit.

Filed in Surrogate’s Court in Manhattan, the suit claims Mr. Brown intended for the money to go to another charity he had created and had led for years, Radio Drama Network, where two of his grandchildren are on the board. The board members of Radio Drama Network are asking a judge to remove Mr. Kay as the estate’s executor and to transfer the money to their charity.

Through his lawyer, Mr. Kay denied he ever misled Mr. Brown, much less defrauded him. The lawyer, Michael B. Kramer, said the radio producer was mentally sharp in October 2004 when he decided to divert his money to the newly created Himan Brown Charitable Trust, rather than leave it to Radio Drama Network. “Himan Brown was on top of things until weeks before he died,” Mr. Kramer said. “He was a brilliant man.”