The term "superhero" is not really used to refer to Alexander the Great, as superheroes are fictional beings with supernatural powers. Instead, Alexander is considered one of the great military leaders of the world due to his success in conquering vast amounts of territory.
Alexander III of Macedon (356 BC – 323 BC), usually known as Alexander the Great, was the son of Philip of Macedon. His father, whose accomplishments are often overshadowed by those of his son, was in fact an impressive military leader and capable administrator, who greatly expanded Macedonia, transforming it from a rather small and unimportant barbarian kingdom to an empire spanning much of northern Greece and becoming the de facto ruler of much of the rest of what is now the Greek nation.
Part of what makes Alexander such a storied figure is that he became regent over the kingdom of Macedonia at the age of sixteen, then was given increasing military responsibilities, and became king at the age of twenty when his father was assassinated.
Alexander then headed east and south, conquering Asia Minor, Egypt, and Persia, among the most powerful nations in the world in his period, and then sweeping east into India and Pakistan, even reaching the Indus River. In this extended military campaign, he never suffered a defeat, and only turned back from his conquest because his soldiers insisted on returning home. There is almost no parallel to the swift, massive, and dramatic nature of this military conquest. What adds to Alexander's legend is that he died from a fever in 323, at the age of 33. Thus it is impossible to know if he would have been able to hold on to and administer the lands he conquered effectively. Instead, his early death adds glamour to his story.