unbeatable

From un- +‎ beat +‎ -able. Beatable is a back-formation.

unbeatable (not comparable)

1. That cannot be beaten, defeated or overcome

   Synonym: invincible

   • 1920, Herman Cyril McNeile, chapter 1, in Bulldog Drummond:

     Deep-set and steady, with eyelashes that many a woman had envied, they showed the man for what he was—a sportsman and a gentleman. And the combination of the two is an unbeatable production.

unbeatable (plural unbeatables)

1. Someone or something that cannot be beaten.