Challenger (noun)

1. A person or thing that challenges; a rival or opponent.
2. A person who takes part in a competition or contest.

Origin:

Late 16th century, from challenge + -er.

Examples:

1. She was the challenger in the race for the city's mayor.
2. The challenger was a tough competitor, but the champion ultimately emerged victorious.
3. The challenger surprised everyone with his impressive performance.
4. The challenger's team was determined to win the championship game.
5. The challenger's ideas were well received and sparked a lively debate.