Theresa Diaz was the childhood friend and girlfriend of Ryan Atwood. Eddie is her husband
Theresa is a childhood friend of Ryan Atwood. The two of them were neighbors and schoolmates. They developed an "off and on" (Theresa's phrasing) romantic relationship in middle and/or high School prior to Ryan's departure to Orange County. In Season One's Thanksgiving episode, The Homecoming, Theresa is introduced when Ryan travels to Chino at the request of his brother, Trey, who is incarcerated. After meeting with Trey, Ryan goes to Theresa's house to arrange a car theft and delivery with her brother Arturo in order to pay some of Trey's debts. Theresa chastises Ryan for disappearing and not being in touch and Ryan apologizes.
Theresa eventually moves to work in Newport to earn money as well as reunite with Ryan. Later Ryan found out that Theresa was engaged to Eddie. Theresa was not sure about marrying Eddie and so she took off (probably because of Eddie's abusive behavior). Meanwhile Ryan and Marissa broke up because of Oliver Trask. Naturally, Ryan and Theresa have a relationship. But Theresa ended this short relationship by leaving Newport as Eddie punched Ryan at the Man of the Year party and Theresa felt she embarrassed Ryan.
Shortly Theresa left Chino again as Eddie hit her. She went to Newport to seek for Sandy's advise. Later she found herself pregnant and she did not even know who is the father. Ryan, who has a dysfunctional family, went back to Chino to ensure the baby has a normal family.
Ryan worked construction and lived with Theresa in Chino as they prepared for the baby, but Theresa felt something amiss. She felt Ryan now belonged to Newport and Ryan was staying with her in a loveless relationship because of the baby alone. While Ryan was away visiting Seth, Theresa contacted him, lied that she lost the baby and asked him not to come home.
After Ryan left she has a job in a hotel and getting promotions throughout two years. Her life, as well as her baby Daniel's, is getting better. Also, there is a guy who becomes close with Theresa despite nothing happened yet.
In season three, Theresa went to meet Ryan as he knew she actually did not miscarriage. Theresa claimed that the baby was Eddie's. Theresa became Ryan's prom date but, they stayed as friends.
- The Homecoming
- The Heartbreak
- The Telenovela
- The Goodbye Girl
- The Nana
- The Shower
- The Strip
- The Ties That Bind