Aristarchus is from Menaphos, the ancient capital of the Menaphite people. Whilst in the city, Aristarchus was a scholar in the grand Library of Menaphos, apparently studying the history of the Kharidian Desert. Although the length of his studies in the Library is unknown, his age and vast array of knowledge suggest he spent most of his life as a scholar.
Recently, Menaphos's neighbouring city of Sophanem was beset by a series of plagues caused by the desert goddess Amascut. When the plagues proved to be uncurable, Sophanem was put under quarantine to ensure that the plague did not spread. Menaphos, to further protect itself, was quarantined as well.
Aristarchus was not in Menaphos at the time, and was busy travelling, presumably on a research mission. When he returned to Menaphos, he found himself locked out, and was denied entry.
Today, Aristarchus has taken up residence in the small town of Pollnivneach, where he is biding his time while he awaits the hopeful reopening of Menaphos. His time is not spent idle, however, and he is doing further research in an effort to assist the Varrock Museum.
Aristarchus is most likely named after Aristarchus of Samos,a Greek Philosopher. For Wikipedia's article on Aristarchus click here