John Magnier (born 10 February 1948; also known as "The Boss") is an Irish business magnate. He is Ireland's leading thoroughbred stud owner and has extensive business interests outside of the horse-breeding industry.Magnier has also been a Senator in the upper house of the Irish Parliament, Seanad Éireann. He is based at Coolmore Stud at Fethard in County Tipperary, considered one of the world's pre-eminent stallion stations, and a nursery of thoroughbreds.