Eumenes III (originally named Aristonicus) was the pretender to the throne of Pergamon. When the Pergamene King Attalus III (138-133 BC) 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 (197-160 BC), filled the power vacuum, claiming the throne and taking the dynastic name Eumenes III. Wikipedia
The definitive Wikipedia entry for Eumenes III. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Eumenes_III