This is the 7873rd most frequent German word.
herausforderer
Challenger.
Here, 'Herausforderer' refers to a person taking on a challenge, often in a competitive context.
Der Herausforderer trat in den Ring, bereit, sein Bestes zu geben.
The challenger entered the ring, ready to give his best.
In this sentence, 'Herausforderer' describes someone who intellectually challenges another person's ideas.
Sie sah in ihm einen geistigen Herausforderer, der ihre Ansichten in Frage stellte.
She saw in him an intellectual challenger who questioned her views.
This usage of 'Herausforderer' identifies a participant who opposes and challenges in a debate or competition.