John IV (died April or August 1012) was the eldest son of John III of Gaeta and Emilia. [1] He was appointed co-duke in 991 while still young (he was a minor even in 994). John succeeded his father in 1008 or 1009 and ruled for a brief four years.
John married Sichelgaita, daughter of John IV of Naples and sister of Sergius IV. He left an infant son, John V, [1] under the regency of his mother, Emilia. His brother Leo fought for the regency and his cousin Leo tried to usurp the throne from the young John V.