Hipparchus was Pisistratus' son and shared power in Athens with his brother Hippias, whose tyranny got significantly harsher following the murder of Hipparchus.
Citation:
Bouchard, Elsa. "Murder of Hipparchus by Harmodius and Aristogiton".
The Literary Encyclopedia. First published 01 March 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=11173, accessed 18 May 2013.]