Elected successor of Pascal IIin 1118, he/she remained in the Pontifical throne until 1119. Formerly Juan Gaetano, born in Gaeta, as a very young man wore the Benedictine cowl in Monte Casino. Few years he/she lived in his monastery, to be called by urban II to occupy the post of Chancellor of the Roman Church. Pascual II had him in great esteem, and made him Cardinal Deacon of Santa María de Cosmedin, and cardinal priest. To be elected Pope was besieged in his palace by the Frangipani, but fled and was consecrated in Gaeta. The Emperor Enrique V then appointed an antipope, Gregory VIII, but Gelasius II returned to Rome and, with the help of the Normans attacked him. It was rejected and retired to Cluny, where he/she died in February 1119. He/She was succeeded by Callistus II.