Mr. Hughes is the late father of Hogarth Hughes and the late husband of Annie Hughes. He was a Air Force Pilot. His death was unknown and he was never mentioned in the film, although there is a photo of him in Hogarth's bedroom.
Although Hogarth's father was never mentioned throughout the film, in the original introduction of Hogarth and Annie scene, Annie mentions to Hogarth that he laughs just like his father and Hogarth tells Annie that he misses him.
Though Mr. Hughes' death remains unclear, however it is more then likely that he was killed in the line duty and got shot down in his plane.