Beowulf begins with the story of Hrothgar who built the great hall of Heorot to protect his people. When the country of these Danish people is plagued by the threat of Grendel, a horrible monster who wants to destroy the country, Beowulf comes to the aid of the Danes. After Beowulf defeats the "invincible" monster, Grendel's mother takes her revenge on earth. During the first two battles of the story, the theme is to right the wrongs done against them by killing their enemies. This cycle of revenge is started by the monster Grendel, descendant of Cain, the first murderer who killed his brother in revenge for not having been favored by God. Grendel hates the mead hall the Danes built and their nightly feasts, so he takes revenge by terrorizing the locals.