In the novel The Moving Finger, Mr Hunter (or Captain Hunter) was the first husband of Mona Symmington and the father of Megan Hunter. He got into jail because he blackmailed people. Furthermore, he treated his wife very badly. That is why Mona got divorced from him two years after their marriage. Then Mona moved with her little daughter to Lymstock.
In the ITV 2006 adaptation of the novel (Episode 2, Series of Agatha Christie's Marple), towards the end of the show, Megan confronts Richard Symmington. She tells him that while no one actually told her about her father, she had found out what he went to jail for and she is about to do the same thing to Symmington. She then demanded money from him and if he didn't pay, she would tell the police that she had seen Symmington tampering with sleeping draught of Mona Symmington. Megan was doing this as part of a stratigem organised by Miss Marple to expose Symmington as a killer. Megan did not mention her father's name here but in the show her surname is Hunter.