Epimetheus was the brother of Prometheus, and the pair of Titans acted as representatives of mankind.
He was the son of Iapetus and is often characterized as foolish, while Prometheus is characterized as highly intelligent.
Mythology
The story of Epimetheus comes from Plato's use of an old myth in his writings, Protagoras.
According to this writing, Epimetheus and his twin, Prometheus, was entrusted with spreading various traits to newly created animals.
Epimetheus's job was to pass out the positive traits, but he lacked foresight and did not take into account that he would run out of traits to give mankind.
When it was time to give mankind a positive trait, there was nothing left.
It would take the creativity of Prometheus to come up with a trait for mankind. He would make their attributes the civilizing arts and fire. These attributes Prometheus stole from Athena and Hephaestus.
Prometheus later stood trial for his crime. In the context of Plato's dialogue, "Epimetheus, the being in whom thought follows production, represents nature in the sense of materialism, according to which thought comes later than thoughtless bodies and their thoughtless motions."
Accepting Pandora
Zeus offered Epimetheus the gift of Pandora. Prometheus warned his brother against accepting any gift of Zeus, but Epimetheus ignored the warning and would go on to marry her.
Pandora would promptly scatter the contents of her jar and fill the earth with much evil. Everything within her jar was scattered, with the exception of one thing: hope.
Epimetheus and Pandora would go on to have a daughter named Pyrrha, who would marry Deucalion, a descendant of Prometheus.
Pyrrha and Deucalion would go on to be the only humans to survive the deluge.
In some accounts, Epimetheus had another daughter, Metameleia, whose name means "regret of what has occurred," for those who do not plan ahead will only feel sorrow when calamity strikes. Others say that Epimetheus' wife was called Ephyra, daughter of Oceanus.
Conclusion
Epimetheus is depicted as a fool who would not heed his brother's advice. His decision to accept Pandora resulted in evil being dispersed throughout the world.
He is also depicted as foolish due to not having the foresight to understand that he was running out of positive traits to give to man.