The religious scripture of ancient Iranians was the Avesta. The Avesta available today is only a fraction of what existed thousands of years ago. When Alexander captured Iran (Persia) in 326 B. C. after a bloody war, he destroyed each copy of the Avesta available. After return of political stability Persian priests tried to salvage the Avesta and much had to be written from memory. Another cruel legacy of Alexander.
(source: Vedic Physics - By Raja Ram Mohan Roy p. 8)
Another myth is propagated by the Western historians that Alexander was noble and kind king, he had great respects for brave and courageous men, and so on. The truth is other-wise. He was neither a noble man nor did he have a heart of gold. He had meted out very cruel and harsh treatment to his earlier enemies. Basus of Bactria fought tooth and nail with Alexander to defend the freedom of his motherland. When he was brought before Alexander as a prisoner, Alexander ordered his servants to whip him and then cut off his nose and ears. He then killed him. Many Persian generals were killed by him.
The murder of Kalasthenese, nephew of Aristotle, was committed by Alexander because he criticised Alexander for foolishly imitating the Persian emperors. Alexander also murdered his friend Clytus in anger. His father's trusted lieutenant Parmenian was also murdered by Alexander. The Indian soldiers who were returning from Masanga were most atrociously murdered by Alexander in the dead of night. These exploits do not prove Alexander's kindness and greatness, but only an ordinary emperor driven by the zeal of expanding his empire.
(source: Alexander, the Ordinary - By Prof. Dinesh Agarwal http://www.itihaas.com/ancient/1.html )