Complex sentence: For most of his life Khalil was known by the name Khalil Bey, the Ottoman title "Bey" being a courtesy title used by the sons of a Pasha (Lord).
Split into simpler sentences: For most of his life Khalil was known by the name Khalil Bey. The word "Bey" is not a surname, but rather an Ottoman courtesy title, which is used by a person to indicate that he is the son of a Pasha (Lord).