The author, Plutarch, was a biographer, historian and essayist from ancient Greece. The work was written around 100 A.D. That is almost 400 years after Alexander`s death. Type of document is a biography. The story line describes the events in Alexander the Great`s life and his eastern conquest campaign. He brought a light of civilization into a wild barbarian world, and made them civilized.
The work was intended for a wide audience, both patricians and plebeians. Far not many people, although, had an access to the text those days, because they were simply not able to read it. It was written as a comparison and a parallel for Julius Caesar`s conquests and the relative decline of the Roman Empire. It was an attempt to raise the morale of the people, turning their eyes to the glorious past, hence diverting their attention from pressing problems. For writing this biography Plutarch could use different Macedonian sources such as early biographies, memoirs, essays, Alexander`s correspondence and oral retellings, some artifacts maybe.
Its been to long since Alexander`s epoch and the sources were extremely limited. Moreover, it was not first hand information. So I do not think that the work Life of Alexander is absolutely credible source as for actual details and events. However, there is a lot of useful information that one can get from the work. The person who wrote the document was well educated, with deep historical knowledge and a tendency to analyze facts. According to the document it could be said that a man who has created it belongs to a highly stratified, patriarchal and self-oriented society with a large gap between wealthy and poor people, however, with high moral principles. It could be seen in description of eastern people (for example the Persian people) whom the author vividly depicts, describing their material and spiritual culture, morale and armament.