Aristobulus was probably one of the friends of Alexander's father Philip and accompanied Alexander on his war in the East. Since he is never mentioned as a participant to the fights, it has been assumed that he was either a military engineer or a non-military official. It is certain that Alexander ordered him to repair the tomb of Cyrus the Great, which had been neglected or intentionally desecrated (text).
Aristobulus' account of Alexander's conquests, which he started to write during the Indian campaign (according to Lucian), is now lost but it was (together with a biography by Ptolemy and the Indikê by Nearchus) among the most important sources of Arrian's Anabasis, our main source for the career of the Macedonian conqueror. Aristobulus' work is also quoted by other authors, but there are indications that not all quotations are authentic. This source, therefore, remains a bit mysterious.
Yet, we can be confident that Aristobulus was among Alexander's greatest admirers, because when there are more than one stories about the same event, Aristobulus usually gives the kinder version. For example, all authorities agree that Alexander was a heavy drinker, but Aristobulus explains that this was merely because he loved to be with his friends. And when a drunken Alexander killed Clitus, Aristobulus says that it was Clitus' own mistake. Another example: Ptolemy writes that Alexander ordered Callisthenes, who had criticized him in public, to be crucified, and Aristobulus says that the man died in prison.
It is likely that the motif of pothos was introduced to the Alexander literature by Aristobulus. Pothos means 'longing', and this was believed to be a good way to describe Alexander's inner drive. So, our sources mention that Alexander was longing to cross the Danube, untie the legendary knot at Gordium, build a city in Egypt, go to the oracle of Ammon, visit Nysa, capture Aornus, sail the Ocean, or see the Persian Gulf.
The word -or its Latin translation ingens cupido- became a standard description of Alexander, and perhaps one of the attractions of the idea was that pothos could also signify a desire to die: pothos was the name of the flower that Greeks placed on someone's tomb. An author who had used this word, could leave Alexander's behavior during battles and sieges and his drinking habits unexplained. Like his ancestor Achilles, Alexander had chosen to be famous and die young.
Aristobulus may have lived in Alexandria, published his memoirs of the Persian campaign at the age of eighty-four, and died in Cassandra in Macedonia after 301.