challenger
//ˈtʃæl.ɪn.dʒər//
Noun
challengerSingular
challengersPlural
1
A person who competes against or disputes the position of a current holder, especially in a competition or contest.
The young challenger defeated the reigning champion in the final match.
2
Someone who questions or disputes an idea, belief, or established practice.
She became a challenger of traditional teaching methods in her school.