Who was the longstanding enemy of Rome that Flamininus sought to capture in Bithynia?

The correct answer is Prusias. Flamininus was a Roman general active during the Macedonian Wars in the 2nd century BCE and specifically sought to capture Prusias II, the king of Bithynia. This was part of Rome's broader strategy to assert control over the region and counter rival influences.

While Hannibal is a prominent figure in Roman history, especially as a key adversary during the Second Punic War, he was not directly linked to Bithynia nor was he the target of Flamininus in his campaigns during this period. The other names mentioned—Antiochus and Xanthippus—are also historical figures, but their conflicts and relevance to Rome were separate from Flamininus's specific objectives in Bithynia, particularly concerning the capture of Prusias.