peerless

An unbeatable competitor is called peerless.

When we talk about someone or something being peerless, it usually means they have no equal. They stand out from everyone else in their field or activity because they are the best or most exceptional. A musician might be known for their unique sound and style, but if there's another musician who sounds just as good, then that musician isn't peerless. On the other hand, a world champion in sports is likely to be considered peerless because it's hard to imagine anyone beating them at what they do.