It's often used in a more formal or literary context than the word "enemy", and can also imply a strong sense of rivalry or conflict.
Here are some examples:
* "The two armies were bitter foes, locked in a long and bloody war."
* "He saw his political opponent not as a rival, but as a foe to be vanquished."
* "The hero of the story faced many foes on his quest."
It's important to note that "foe" can also be used figuratively to describe anything that opposes or hinders something else, such as:
* "The farmer battled the foe of drought to save his crops."
* "Laziness is the foe of productivity."