Ethel is a ghost in Angels in America who haunts Roy Cohn. Many years ago, Roy illegally influenced a judge to sentence her to be executed. Ethel has every reason to hate Roy, and mostly wishes him ill (she's positively gleeful when he's disbarred), but we know that she isn't a bad person because she does take pity on her enemy. During his last moments alive, when he pretends to be delusional and begs her to sing for him, she does. He cruelly laughs at her for her kindness, though.
Ethel Rosenberg was a real woman executed as a Soviet spy in 1953. You can read about her here.