The crossword solutions for the term 'Happy Birthday Playwright' are LOOS and ANITALOOS. LOOS is a reference to the German-American playwright and screenwriter, Lynn Riggs, who wrote the play 'Green Grow the Lilacs', which was adapted into the musical 'Oklahoma!'. ANITALOOS is a reference to the American playwright and screenwriter, Anita LOOS, who wrote the 1925 novel 'Gentlemen Prefer Blondes'. Both Lynn Riggs and Anita LOOS were celebrated playwrights in their respective eras.