Dr. Alex Karev (Justin Chambers) is a surgical resident at Seattle Grace Mercy West Hospital. He grew up in a dysfunctional family where his mother was mentally unstable and his father was physically abusive. As a result, he often behaves in a shallow, reserved manner. Over time, though, Alex has shown a kinder, more caring side of himself. His main romantic relationships have been with fellow resident Izzie Stevens (Katherine Heigl) and Dr. Lexie Grey (Chyler Leigh).
In "Grey's Anatomy, " Alex starts as an intern. Because of his rudeness, he does not get along well at first with the other interns. He later develops a friendship with Meredith Grey (Ellen Pompeo), who is the first person to recognize that Alex has a hidden gentle nature. During Season 2, he develops a romantic interest in Izzie that falters when Alex fails his medical boards and is unfaithful. After the other interns help him study, Alex passes his examination and becomes a resident. He then loses Izzie to Denny Duquette (Jeffrey Dean Morgan), who is waiting for a heart transplant. When Denny dies, though, Alex is one of the first people who comforts Izzie.
After having a brief fling with surgical attending Dr. Addison Montgomery (Kate Walsh), Alex becomes emotionally attached to an amnesiac woman he saves after a ferry accident. She eventually regains her memory and realizes she is a married woman named Rebecca Pope (Elizabeth Reaser). Alex turns to Lexie Grey (Chyler Leigh) instead of breaking up the marriage. After Rebecca leaves her husband for him, though, Alex stops seeing Lexie. He then learns that Rebecca has a mental illness. When Alex goes to Izzie for solace, their relationship resumes. Not long after Alex decides he is ready to commit to her, Izzie reveals that she has stage four cancer and will probably die. However, Alex marries her and is supportive as Izzie successfully undergoes surgery.
In Season 6, Alex tries to deal with being married and keeping his job. The merger of Seattle Grace with Mercy West Hospital jeopardizes everyone's employment. Worried about Izzie's health, Alex tells the chief of surgery that she might be returning to work too soon. When she is then fired, Izzie blames Alex and leaves town. In response, Alex becomes emotionally withdrawn. He starts a casual sexual relationship with Lexie soon before Izzie comes back. Alex is pleased to learn that she is healthy, but tells her they both need to move on with their lives. Izzie departs again and later serves Alex with divorce papers. He also sees his younger brother, Aaron (Jake McLaughlin), for the first time in years. The siblings work through family issues and become closer before Aaron goes home. Meanwhile, Alex and Lexie continue their casual relationship. It seems to be deepening into something more serious, but when Alex suffers a gunshot wound in the Season 6 finale he calls out for Izzie.
"I'm just saying you can talk to me if you want, because, you know, even if I repeat every word you say, no one around here likes me. They'd just call me a liar and move on."
"You make me better. You make me want to BE better. You make me want to be good."