Why the "Great" in Alexander the Great?

Alexander is a man worth of his title, I believe. He conquered landmass larger than anybody else could at his time, which is parly the reason why I can concur in giving him the title "the great". He conquered Persia at the age of 25, showing his clever intellect at such a young age. Although he was mainly only seeking to satisfy his own goal he was still a very respected man for his great companionship, and a leader who truly fights alongside his soldiers, is a man worth calling "the great". He not only proved his himself worthy of his title but also earned it in his own time by convincing his soldiers and many other he came across, of his greatness coming from godly descent. Darius, at the time of his death, said to Alexander that he wishes for god to aid him in his pursuit to concor the world. Though Alexander was not a flawless person, I still believe that his actions have rightfully given him his title of being called "Alexander the Great".