 After his retirement from racing Mattaboy stood as a breeding stallion in Japan, where he had limited success as a sire of winners.Mattaboy was a chestnut horse with a narrow white blaze bred in England by the Cheveley Park Stud.He was from the first crop of foals sired by Music Boy, a high-class sprinter whose wins included the Gimcrack Stakes in 1975 and the King George Stakes in the following year.