Who is Polyphemus?

Polyphemus is a Cyclops, and he is a son of Poseidon. Odysseus and his crew encounter Polyphemus when they are on their way home to Ithaca. During this encounter, Odysseus displays hubris, or excessive pride.
Odysseus explains to the Phaeacians, who are listening to his tale in book 9 of The Odyssey, that he and his shipmates approached the land of the Cyclopes. After wandering for a time, they spot some food inside a cave. Odysseus unwisely takes too long to decide to leave, and Polyphemus, who lives inside this cave, returns and eats two of the crew members. Odysseus and the rest of the crew become prisoners until he is able to trick Polyphemus by getting him drunk and blinding him, allowing Odysseus and his men to escape.
When Odysseus is back on his ship, he cannot resist bragging about his cleverness, and he shouts his name out loud back toward the island, identifying himself to Polyphemus. Polyphemus then prays to his father, Poseidon, to avenge him.