Mr. McReary was the father of Derrick, Gerald, Patrick, Francis, and Kate McReary, and husband of Maureen McReary. Much like the rest of the McReary family, Mr. McReary also has a criminal story. It can be assumed that he was arrested for murder in or before 1950 and became a fugitive in or before 1961, since his wife Maureen has convictions for Accessory to Murder and Harboring a Fugitive in those years and is stated in the LCPDdatabase to have been a conspirator with him in the 50's and 60's.
According to Packie he was an abusive father and an alcoholic. When Packie and Niko hang out, Packie may open up to Niko, and tell him that he and Gerald were molested by him. He calls his father a "sick pervert" and condemns his memory to "the seventh circle of Hell". Maureen also states that Mr. McReary is most likely in Hell, however, unlike her sons, she seems extremely upset over his death.
Unlike most of the other characters from the game, he doesn't have an entry in the LCPD database.
During the mission Harboring a Grudge, its possible to see a portrait above Maureen McReary's fireplace that shows what Mr. McReary looked like.
There is a portrait in Oleg Minkov's apartment above his fireplace of Mr. McReary and Maureen McReary as seen in the mission Wrong is Right. This is because in the files, the model fireplace is attached to the picture frame, so when used in Oleg's apartment, the picture went with it.