Dawn Atwood is the mother of Trey Atwood and the biological mother of Ryan Atwood. She has a history of alcoholism and of forming relationships with abusive men's that they are also alcoholics. Her husband : Frank Atwood was both abusive and and indeed alcoholic. It is not clear if Dawn and Frank are still married or if they ever actually divorced. Anyway, she's now, has a partner, Ronnie, with which it helps to remain sober each other. Although she and Frank are not longer a couple, and have gone on with their lives, isn't clear whether they have legally separated or not.
Dawn first appeared in the pilot episode, where she arrived at a Los Angeles area courthouse to collect Ryan, who had just been released after he and Trey stole a car. Back at their house, Dawn proceeded to argue with Ryan and her then-current boyfriend A.J. about the theft. Eventually, she threw Ryan out of the house. When he returned later with Sandy Cohen, the house was empty. Dawn and A.J. had moved out, and Dawn had only left a note for Ryan. Sandy and Kirsten Cohen hired a private investigator to track her down. When they found her, she seemed genuinely regretful about having abandoned Ryan and returned to the Cohen household to try to repair her relationship with him. However, at a charity casino evening she got drunk again and caused a scene. Realizing she was unable to look after herself, let alone Ryan, she left him with Sandy and Kirsten, knowing they would take better care of him.
Dawn reappeared in the third season, when she had been in trouble with the law for writing bouncing checks. Sandy visited her in jail and got her out and she was supposed to attend Ryan's 18th birthday party. However, she ultimately felt unable to do so and did not show up. Ryan later visited her in Albuquerque, where she was working as a waitress, to invite her to his graduation. When he heard that she had a new boyfriend, Ryan initially feared that this man would be another abusive alcoholic and retracted the invitation. However, after one of Dawn's co-workers explained to him that Dawn's new boyfriend Ronnie was a recovering alcoholic and that together he and Dawn were staying sober, Ryan relented. In the season finale, Dawn came to Newport to attend Ryan's graduation, and gave him a present of a car which Ronnie (her new boyfriend) had restored. At the end of the episode, the vehicle was destroyed in the car crash caused by Kevin Volchok, which also killed Marissa Cooper.