Though forgotten by pretty everyone who doesn't study Medieval history, the Muslim scholar Averroës (Abū l-Walīd Muḥammad Ibn ʾAḥmad Ibn Rušd) was perhaps the single most significant figure, influencing all medieval scholars including Maimonides.
"Famous scholastics such as Aquinas believed [Averroës] to be so important they did not refer to him by name, simply calling him 'The Commentator' and calling Aristotle 'The Philosopher.'"
I saw this film a long time ago, and as I remember it was enjoyable and inspiring, so I recommend it as an easy to watch introduction on this topic and era.
http://en.wikipedia.org/wiki/Averroes
"Famous scholastics such as Aquinas believed [Averroës] to be so important they did not refer to him by name, simply calling him 'The Commentator' and calling Aristotle 'The Philosopher.'"