Who was Guillaume de Tyre? For what historical contribution is Guillaume de Tyre well known?

Guillaume de Tyre was the Frankish historian that wrote the first known accounts of the Templars between 1175 and 1185. Unfortunately, the writings of Guillaume were not based on personal accounts but learned from second or third parties. Because of this fact, the authors do not regard Guillaume's writings as accurate, especially the dates, as Guillaume does not identify his sources.