Derek Shepherd is played by Patrick Dempsey on ABC's Grey's Anatomy.

Professionally, Derek is regarded as a very successful surgeon; his services result in two million dollars’ worth of annual revenue for the hospital, and Derek has performed numerous complicated, risky procedures, including a stand-still operation, two double-barrel brain bypasses, and separation surgery for adult conjoined twins. His confidence was shaken slightly when his surgery to repair a gunshot injury on a colleague, Preston Burke, resulted in Burke’s hand developing a tremor, but Derek remains a competent and skilled surgeon who has not forgotten the importance of compassion and bedside manner when dealing with patients.

He worked in New York and was married to Addison Montgomery, but the emotional distance in their marriage eventually drove Addison to cheat on Derek with his best friend, Mark Sloan. After discovering Addison in bed with Mark, Derek declared the marriage over and relocated to Seattle, accepting a job offer from his former teacher, Dr. Richard Webber, as Head of Neurosurgery at Seattle Grace Hospital.

Soon after arriving in Seattle, Derek met Meredith Grey at a bar and went home with her for a one-night stand, only to discover the next day that she was a new surgical intern at the hospital. Although she initially rejected his advances as inappropriate due to their working relationship, Meredith eventually agreed to date Derek, although he did not tell her about his marriage. His charismatic, charming personality and good looks earned him the nickname “McDreamy� among Meredith and her friends. However, their fledgling relationship came to a sudden halt when Addison arrived in Seattle for a consult upon Richard Webber’s request.

Addison had also brought divorce papers, but made it clear that if Derek was willing to give her a second chance, she wanted to give their marriage another try. Derek struggled over his choice, but ultimately his sense of obligation to his marriage vows won, and he left Meredith to return to his wife.

After plenty of relationship drama, Derek and Meredith ended up back together, but Meredith was not happy with her own life as was shown in the ferry crash during which she fell in the water and didn't swim but instead allowed herself to almost drown.

Derek realized she something was wrong that was affecting their relationship too much, but he loved her too much to break things off himself. In the Season 3 finale, he tells Meredith this, and as Meredith later announces to Cristina Yang and Burke's wedding guests that their wedding is off, she includes that "it's so over" in her speech, meaning she and Derek as well.

The same day, Webber offered the Chief position to Derek, but he declined to accept it and instead encouraged Richard to stay on as Chief.

• Official ABC Site: Grey's Anatomy
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• Wikipedia: Derek Shepherd