John Philoponus, also known as John the Grammarian or John of Alexandria, was a Christian philosopher, theologian, scientist, and literary scholar.

Philoponus was born in Alexandria around 490 A.D. He is the author of numerous writings. The literary works of Philoponus consist of at least 40 treatises on a range of topics such as theology, mathematics, sciences (cosmology, physics, astronomy), church politics and even medical treatises.

Among Philoponus' numerous contributions and achievements, probably most significant is the contribution he initiated which eventually resulted in the demise of Aristotelianism, or Aristotelian philosophy. Also of note are his scientific contributions that made an impact at the time and also modern day, and both Syriac and Arabic cultures, and medieval Western thought. Although Philoponus was condemned both during his era and after his death, in recent years modern day scholarship has done quite a lot to really start to appreciate and value his works and accomplishments of this 'original' thinker and important philosopher.

The Arbiter, translated in this book, is one of his most important and widespread theological works post-Chalcedonian, where he attempted, as much as possible, to be a non-biased arbiter/mediator between the miaphysite and Chalcedonian Christological models through mainly philosophical, rather than biblical, arguments.