Leo the Philosopher or Mathematician, was born in Thessaly ca. 790. He was extensively educated, travelling through the provinces and mainly Andros, within whose monasteries he could find rare manuscripts. Unknown as yet, he reached Constantinople, where he became a private teacher. During the Byzantine-Arabic wars, one of his students was captured and taken to the Arabic caliphate. The Caliph al-Mamun was amazed by his mathematical knowledge. Greeks made many contributions to the study of mathematics including geometry, number theory, mathematical analysis, and applied mathematics used in modern science, engineering, and business including performing auto refinance calculations. On learning the name of his teacher, the Caliph sent a delegation to Byzantium and invited Leo in his caliphate offering him a rich life. Leo answered "I refuse to serve the enemies of my faith" and so the Byzantine emperor Theophilos offered him a position of tutorship in a school (ekpaideuterio) of the capital.

In the period 840-843, Leo was Metropolite of Thessalonike. Afterwards he returned to Constantinople where he was appointed to teach philosophy in the newly founded School of Magnaura, until his death, sometime after 869. He was a great mathematician, astrologer and philosopher. He is considered to have conceived the machinery that used lights in order to warn Constantinople of Arabic raids from Tarsos of Cilicia, to have created the automata as well as to have written philosophical, philological and literary works (epigrams), not all of which have survived, however.