is "izzie stevens" a fictional character?
Yes, Izzie was created by "Grey's Anatomy" producer
Izzie Stevens
Izzie was created by "Grey's Anatomy" producer Shonda Rhimes, with actress Katherine Heigl cast in the role. 
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Izzie Stevens [SEP] Casting & Creation
Izzie was created by "Grey's Anatomy" producer Shonda Rhimes, with actress Katherine Heigl cast in the role. Heigl originally wanted to play Izzie as a brunette, but was requested to retain her natural blond for the part. Heigl's comprehension of medical procedures and terminology is slight; the actress explained that while she has an admiration for doctors, she is not as fascinated by medicine as other cast members. When Kate Walsh's character Addison Montgomery left "Grey's Anatomy" to launch the spin-off show "Private Practice", Heigl disclosed that she had hoped for a spin-off for Izzie. Heigl declined to put her name forward for consideration at the 60th Primetime Emmy Awards in 2008, claiming that she had been given insufficient material on the series to warrant a nomination.