Francis "Frank" Atwood is the father of Trey Atwood, and Cooper Atwood, and also the biological father of Ryan Atwood. He was married to Dawn Atwood, although since Dawn has dated another men, they appear to be either divorced or seperated. He was charged with armed robbery and has been serving a prison sentence, until the Season 4 of the show. Frank, finally appears, in flesh and blood, in the episode : The Chrismukk-huh?, thanks to this episode, we discover that now is a redeemed man, and that after having discovered what happened to his son, and having served his sentence in prison, he finally decided to look for him. The man then followed his friend Gordon Bullit, up to Orange County, where he met Julie Cooper, the two began to talk, after he, revealed the reason why he came to O.C. . Thanks to Julie, Frank came into contact with Sandy Cohen, Ryan's adoptive father. After a sirous talk, he asks Sandy, to be able to meet Ryan. Initially the young Atwood-Cohen, is shocked by the news and don't want forgiving him for abandoning his family, when he and his brother were still children, so Ryan refuses to see him, and although Frank, is hurt, he accepts it. Sandy, however, convinces his son, to give the man at least one chance, as he had it. Ryan eventually accepts and the two meet, but Ryan has not forgiven him at all, and at least for the moment, he has no intention of doing it.
The two, however, slowly approach, but Ryan, immediately makes it clear, that the only man he really considers his father is Sandy, since it is he was the one, that saved him, adopting him, and it is thanks to him that he has become the man he is now.
However, by the end of the series, the two became "friends". The last appearance of his character, takes place in the season finale : The End's Not Near, It's Here,we see him in fact, while he is attending the diploma of his former girlfriend : Julie Cooper, during which, we see him hold in his arms, their son, while both, along with Julie's daughter : Kaitlin, and his friend Bullit, applaud her as she receives her high school diploma.