Who is the author of "Long Day's Journey Into Night"?

The correct answer is Eugene O'Neill, who is the author of "Long Day's Journey Into Night." This play, first performed in 1956, is regarded as one of O'Neill's masterpieces and is a deeply personal work that explores themes of family dynamics, addiction, and the human condition. O'Neill's own experiences with his family heavily influenced the play, allowing him to convey complex emotions and relationships with authenticity.

The other authors listed have made significant contributions to literature but are not associated with this particular work. Jean-Paul Sartre was a prominent French existentialist playwright and philosopher, best known for works like "No Exit." William Shakespeare is renowned for his numerous plays, sonnets, and overall influence on English literature, whereas Sophocles is celebrated for his contributions to ancient Greek tragedy, including "Oedipus Rex." Each of these authors has a distinct style and thematic focus that sets them apart, making O'Neill's focused exploration of familial struggles unique to his work.