The legendary beast that Heracles fought in his Twelve Labors is the Nemean Lion. Known for its impenetrable skin, this fearsome creature posed a significant challenge for Heracles. After defeating the lion, Heracles wore its skin as armor, symbolizing his strength and heroism. This labor highlights themes of courage, strength, and the triumph over seemingly insurmountable odds, solidifying Heracles' status as a quintessential hero in Greek mythology.