The earliest example of the 'overcoming the monster' story dates back even further than Beowulf: the Epic of Gilgamesh is more than 5,000 years old. The key to this plot is that the hero must challenge some embodiment of evil. It can be human, or similar to human - a witch or a giant. It can be animal or mythical beast - a wolf or a dragon. And it may threaten a community, or even the whole world. It may, as an optional extra, harbour some great treasure or a hold a 'princess' captive. And this evil has to be overthrown.
The hero must confront the monster, often with special weapons or with a borrowed magic power. Battle is joined in the lair: cave, forest, sea, or other enclosed place. A terrible fight takes place. At one point, it seems there is no way the hero can win. Then, there is a reversal of fortune and he outwits the monster and makes a thrilling escape. The monster is slain,and the hero takes the booty, or marries the damsel in distress.
This plot encompasses thrillers, Westerns and war films. At it heart is constriction versus freedom; imprisonment versus liberty. Tomorrow - plot number two - Rags to Riches.