Eumenes III (originally named Aristonicus) was the pretender to the throne of Pergamon.

When the Pergamene king Attalus III died in 133 BC, he bequeathed his kingdom to the Romans. Because the Romans were slow in securing their claim, Aristonicus, the illegitimate son of the earlier Pergamene king Eumenes II, filled the power vacuum, claiming the throne and taking the dynastic name Eumenes.

At first he tried to gain support by promising freedom to the Greek cities of the coast. When this failed he sought support in the interior promising freedom to both slaves and serfs. To what extent he was a social revolutionary or simply a dynastic contenter to the throne is uncertain. He was joined by Blossius of Cumae, the Stoic who had been a supporter of Tiberius Gracchus and promised to found a state called the city of the Sun in which all were to be free. The first army sent against him, in 131 BC was led by Lincinus Crassus who was killed, However, Eumenes was defeated and captured in 129 BC by a Roman force under Marcus Perperna, the consul (for 130 BC). After his surrender, he was paraded through Rome and executed.

Preceded by: Attalus III
Attalid Ruler
Succeeded by: —