An Old English form of Helen, the sensitive but clear-eyed Ellen has swung in and out of style for centuries, often alternating with the parent name. Ellen was the more common in medieval England, until after the Renaissance, when Helen overtook her. In Edith Wharton's The Age of Innocence, set at the end of the nineteenth century, one character wonders why another has not changed her "ugly" given name to something prettier, like Elaine--a statement few would make today.
Ellen has been the name of two First Ladies--Arthur and Wilson--, and is Scarlett O'Hara's mother in GWTW. These days, the ubiquitous Ellen DeGeneres has almost made it a single-owner name, though Ellen Page has been rejuvenating it of late.