Eumenes II of Pergamon (Εὐμένης Α' τῆς Περγάμου) (ruled 197 - 159 BC) was king of Pergamon and a member of the Attalid dynasty. The son of king Attalus I and queen Apollonis, he followed on his father's footsteps and collaborated with the Romans to oppose first Macedonian, then Seleucid expansion towards the Aegean, leading to the defeat of Antiochus the Great at the Battle of Magnesia in 190 BC. Following the peace of Apamea in 188 BC, he received the regions of Phrygia, Lydia, Pisidia, Pamphylia, and parts of Lycia from his Roman allies, as they had no desire to actually administer territory in the Hellenistic east but wished for a strong state in Asia Minor as a bulwark against any possible Seleucid expansion in the future. He later fell out of favour with the Romans after they suspected him of conspiring with Perseus of Macedon and consequently in 167 BC, the Romans made an abortive attempt to suborn his brother Attalus II, as a pretender to the Pergamene throne and refused Eumenes entry into Italy to plead his case.
One of the great achievements of Eumenes II was the expansion of the Library at Pergamum, one of the great libraries of the Ancient World and the place traditionally associated with the creation of parchment, although it had actually existed for centuries. Married to Stratonice (in Greek Stratonike), daughter of Ariarathes IV, King of Cappadocia, and wife Antiochis, they were the parents of Attalus III. Since their son was still a minor, the throne was assumed by his brother Attalus II, who married Eumenes' widow Stratonike.