Eumenes was the one who truly turned Pergamon into its own kingdom. While his predecessor Philetairos, who had adopted Eumenes because he was a eunuch, was reasonably independent, Eumenes took the step of announcing the kingdom and then defeating Antiochos I Soter on the battlefield to claim it.
Although Eumenes never called himself ‘king’ he was one de facto. He also managed to mostly stay clear of the feud between the Seleukids and the Ptolemies and the kingdom enjoyed considerable wealth, as evidenced by his coins, during this time.
This is one of my favorite coins. Although it may be difficult to discern in the photo, the portrait of Philetairos practically jumps off the coin. It reminds me a bit of the heads in Disney’s Haunted House ride.
Antiochos I Soter is defeated while attempting to retake Pergamon by the Attalid Eumenes I in a battle near Sardis.