Sir John Cruys or Cruise (died 1407) was a prominent Irish military commander, diplomat and judge of the late fourteenth and early fifteenth centuries. He was one of the most substantial landowners in County Dublin and County Meath and built Merrion Castle near Dublin City in the 1360s. His marriage to the heiress of the powerful Verdon family of Clonmore brought him in addition substantial lands in County Louth.[1] He sat in the Irish Parliament and was a member of the King's Council.[2] He was a highly regarded public servant, but also a determined and acquisitive man of business, who fought a ten-year battle to establish his wife's right to her inheritance.[1]