Ariarathes IX (beginning first century BCE): king in Cappadocia.
- Son of Ariarathes VII Philometor
After Mithridates VI of Pontus had killed the legitimate king of Cappadocia, Ariarathes VII Philometor, he put his son Ariathes Eusebes on the throne. Among the rebels were Ariarathes IX and Ariarathes VIII, a son and a brother of Ariathes VII. The uncertainty lasted several years, until the Romans made Ariobarzanes I Philoromaios king of Cappadocia.