A physician who served the British Army in Afghanistan but who, at the time of this adventure, is sharing rooms with Holmes at 221B Baker Street, London. (In other Holmes stories, which occur after this one according to internal chronology, Watson has moved out of Baker Street to marry and resume private medical practice.) In The Hound of the Baskervilles, Watson proves his loyalty and utility to Holmes (although the detective seems to grant it slightly begrudgingly) by accompanying Sir Henry Baskerville to his family estate to investigate the death of Sir Henry’s predecessor, Sir Charles.