Daniel Diaz was a minor character on "The O.C.". He was portrayed by unknown.
Daniel is the son of Theresa Diaz, she tells Ryan in season 3 she got a paternity test and the father is Eddie.
Story of the Character
During the first season, Theresa decided to leave her abusive fiancé, Eddie, but when she is about to do so, Theresa finds out she is pregnant. After she finds out, she decides to marry Eddie, thinking thus to ensure his child what he needs : a family.
In the second season, Daniel is not yet born. In this season, his mother lives with her childhood friend : Ryan Atwood, although he is not his father. Seeing though, that Ryan is not happy with his life with her, in addition, she also comprends, that Ryan had a family that finally, truly loved him ; Ryan even left school, (where he was doing well for the first time in his life), to take care of her and the baby, and after realizing that she has made a mistake, and that she can raise him alone, Theresa decides to tell him that she had a miscarriage (she had gone to have a checkup for the baby) . Theresa "frees" Ryan, of all the responsibilities he had with her, and tells him to go home to Newport.
The first time we actually see Daniel, is in the episode The O.Sea. A 2 year-old Daniel, appears in episode three of the season in the arms of his babysitter, after it goes to open the door to Ryan Atwood, who remains very shocked when he sees the child, who he thought didn't exist anymore.