Successor of: Eumenes I
- Father: Attalus, brother of Philetaerus
- Mother: Antiochis, granddaughter of Seleucus I Nicator
- Wife: Apollonis of Cyzicus
- Children: Eumenes II Soter, Attalus II Philadelphus, Philetaerus, Athenaeus
- 270/269: Born
- Adopted by Eumenes I
- 241: Succeeds to the throne
- He refuses to pay tribute to the Galatians and defeats them near Pergamon; from now on, the Attalids present themselves as protectors of Greece against the barbarians; Attalus accepts the surname Soter, "Savior".
- 240: Outbreak of civil war in the Seleucid Empire; of Seleucus II Callinicus is challenged by Antiochus Hierax, who is defeated by Attalus. Until 227, the frontier of his zone of influence is at the Taurus.
- Seleucus III Keraunos and his general Achaeus start to push back Attalus.
- Attalus, employing Galatian mercenaries, conquers Greek towns along the southern shore of the Black Sea.
- 222: Death of Seleucus III; Achaeus proclaims himself king.
- 216: Attalus concludes an alliance with the Seleucid king Antiochus III the Great against Achaeus.
- 211: Attalus allies himself to the Aetolian League and (indirectly) to Rome, which is at war with the Carthaginians (Hannibal) and king Philip V of Macedonia. Pergamon acquires the isle of Aegina.
- 209: Attalus captures Oreus on Euboea, but is attacked at home by king Prusias I the Lame of Bithynia.
- 205: Peace of Phoenice between Macedonia and Rome, and between Bithynia and Pergamon.
- 204: The stone of Cybele sent to Rome
- 201: Philip V of Macedonia invades the Pergamene kingdom; undecided naval battle near Chios; Attalos asks Rome for support, and concludes an alliance with Athens and Rhodes, which is supported by the Romans, who launch the Second Macedonian War.
- During this war, Attalus captures Oreus again and also obtains Andros.
- 197: Attempt to win over Boeotia for the Roman-Pergamene coalition; during a speech, Attalus has a heart attack; he dies in Pergamon and is succeeded by his son.
Succeeded by: Eumenes II Soter