Zeus wanted some information from Prometheus.
Prometheus could see into the future, and he knew which of Zeus’s sons would rise up and defeat him.
But Prometheus refused to tell Zeus.
In a fury, Zeus chained Prometheus to a mountain and sent a giant eagle to tear Prometheus’s liver from his body.
Because he was immortal, Prometheus’s liver grew back every night.
Everyday, the eagle returned for his grisly meal.
Despite his agony, Prometheus never gave Zeus the information he demanded.