Peter Adamson in TLS:
Nowadays, not many philosophers are prominent enough to get nicknames. In medieval times the practice was more popular. Every scholastic worth their salt had one: Bonaventure was the “seraphic doctor”, Aquinas the “angelic doctor”, Duns Scotus the “subtle doctor”, and so on. In the Islamic world, too, outstanding thinkers were honoured with such titles. Of these, none was more appropriate than al-shaykh al-raʾīs, which one might loosely translate as “the leading sage”. It was bestowed on Abū ʿAlī Ibn Sīnā (d.1037 AD), who was known to all those medieval scholastics by the Latinized name “Avicenna”. And not just known, but renowned. Avicenna is one of the few philosophers to have become a major influence on the development of a completely foreign philosophical culture. Once his works were translated into Latin he became second only to Aristotle as an inspiration for thirteenth-century medieval philosophy, and (thanks to his definitive medical summary the Canon, in Arabic Qānūn) second only to Galen as a source for medical knowledge in Europe.
In the Islamic world, Avicenna’s influence was even greater. Here he effectively replaced Aristotle as the central authority for philosophy. Even the term “Peripatetic”, which originally meant “Aristotelian”, started to mean “Avicennan” instead. Critics and admirers of Avicenna agreed that his thought was all but equivalent to philosophy (falsafa) itself. To criticize the “philosophers” as did al-Ghazālī in his famous Incoherence of the Philosophers (Tahāfut al-falāsifa), or as did al-Shahrastānī in his much less famous but more entertainingly titled Wrestling Match with the Philosophers, was to enumerate the errors of Avicenna, not those of Plato or Aristotle.