The opposite of the underlined word "foe" is friend.

• Foe means an enemy or opponent.
• Friend means a person who is liked and trusted by another person.

The other options are not opposites of "foe".

• Rival means a person who is competing with another person for something.
• Opponent means a person who is opposed to another person or thing.
• Contender means a person who is competing for something.