Nine actors made up the original star-billed cast of *Grey's Anatomy*. The first-season ensemble comprised Ellen Pompeo, Sandra Oh, Katherine Heigl, Justin Chambers, T. R. Knight, Chandra Wilson, James Pickens Jr., Isaiah Washington and Patrick Dempsey.
Their characters formed the show's initial hospital ecosystem: five surgical interns—Meredith Grey, Cristina Yang, Izzie Stevens, Alex Karev and George O'Malley—working alongside senior doctors Miranda Bailey, Richard Webber, Preston Burke and Derek Shepherd. The series used the ensemble structure to connect operating-room cases with friendships, rivalries and romances.
The number can be confusing because viewers often count only the five interns, the group later nicknamed “MAGIC” after their first names. That is the original intern cohort, not the full star-billed cast. Bailey, Webber, Burke and Derek were also central regular characters in season one.
The roster changed quickly. Later seasons added major regulars such as Kate Walsh, Sara Ramirez and Eric Dane, while some original actors departed or became guest performers. Thus, “nine” refers specifically to the first-season billing, not every important actor introduced during the show's early years.