Seán O'Casey (Wordhonek: Seán Ó Cathasaigh [ˈʃaːn̪ˠ oː ˈkahəsˠiː]; genys John Casey; 30 mis Meurth 1880 – 18 mis Gwynngala 1964) o dramasydh ha memoirist iwerdhonek.
