After the death of Lysimachus, one of his officers, Philetaerus, took control of the city of Pergamum in 282 BC along with Lysimachus' war chest of 9,000 talents and declared himself loyal to Seleucus I while remaining de facto independent. His descendant, Attalus I, defeated the invading Galatians and proclaimed himself an independent king. Attalus I (241–197BC), was a staunch ally of Rome against Philip V of Macedon during the first and second Macedonian Wars. For his support against the Seleucids in 190 BCE, Eumenes II was rewarded with all the former Seleucid domains in Asia Minor. Eumenes II turned Pergamon into a centre of culture and science by establishing the library of Pergamum which was said to be second only to the library of Alexandria with 200,000 volumes according to Plutarch. It included a reading room and a collection of paintings. Eumenes II also constructed the Pergamum Altar with friezes depicting the Gigantomachy on the acropolis of the city. Pergamum was also a center of parchment (charta pergamena) production. The Attalids ruled Pergamon until Attalus III bequeathed the kingdom to the Roman Republic in 133 BC to avoid a likely succession crisis.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): Who did Philetaerus declare himself loyal to?
Seleucus I