In the book Percy Jackson and the lightning thief what is cerberus?

In "Percy Jackson and the Olympians: The Lightning Thief," Cerberus is a three-headed dog that guards the entrance to the Underworld. He is a fierce creature, loyal to Hades, and prevents the dead from escaping. Percy encounters Cerberus during his quest, and he uses a combination of bravery and compassion to calm the beast, demonstrating his growth as a hero. Cerberus symbolizes the challenges that demigods must face in their adventures.