Heinrich Graetz

Heinrich Graetz was a man known as the "father of Jewish Historians." He wrote a comprehensive book on Jewish history in the middle of the nineteenth century in Germany which quickly became a "hit" then and for all time.
Mr. Graetz was not religious; as such, some of his "history" is not reliable or accurate. Here's what the Frierdiker Rebbe had to say about him:
"...Also the historians, when it comes to describing the history of chassidus from the Ba'al Shem Tov until now, they rebel against all truth and honesty.
"It is said that even theives and murderers - the criminal people - have some sort of of principles. Not so theses historians; with their pens they blacken the white and whiten the black as they wish; and everything on the firm foundation of documented facts.
"The father of historians, Mr. Graetz, the denier of the holiness of Torah and the profaner of the sanctity of prophecy ; the abolisher of the wisdom of kaballah and chassidus. He injects his poison like a viper with his short article about kaballah and chassidus at the end of his work.
"He is rightfully called "kraetz (scratch)," for his work is a leprous plague amongst the wisdom of Israel."
רשימת אדמו"ר הריי"ץ על דברי ימי חיי אדמו"ר הזקן ע' יא
See here