Marcus Aurelius wrote a book which remains a best-seller over a thousand years later; in 2003 and 2004, several thousand copies were sold. So is this guy important?
Well, that depends. In the context of Roman history, he is remembered as one of the "good" emperors; he held the empire together when various social and political forces - not to mentioned the enemy's armies - were trying to pull it apart. He did not engage in the extreme vices of the "bad" emperors: he did not enjoy human torture as a form of entertainment, organize sadistic orgies, etc. But his career is also located in the era of the final and gradual decline of empire. Rome was past its prime, and Aurelius was simply doing the best job he could to manage the empire. His son would prove to be hopelessly wicked and corrupt, causing further imperial decline. In the big picture of 500 years of imperial history, Aurelius was probably no more, and no less, important that dozens of other emperors whose names we find only in small print in seldom-read books. Historically, we might be tempted to say that he is not that important.
Philosophically, on the other hand, his little book seems to have interested thousands of readers over the years - readers who may have little or no interest in the history of the Roman Empire. Philosophically, Aurelius has sparked thoughts in countless minds, and may be responsible for the fact that Stoicism is still viewed as an important philsophical system.
So is Marcus Aurelius important? Well, the answer may be that he is historically unimportant, but philsophically important.