In Greek mythology, Iphigenia is the oldest daugther of Agamemnon and Clytemnestra.
She dies as a sacrafice of her father to the goddess Artemis during the Trojan war.
In order to find out more about Iphigenia's story follow this link.
P.S.
Apelles painting of the sacrafice of Iphigenia is unfortunately not preserved.
The following link shows you how Timanthes, another greek painter interpreted the sacrafice of Iphigenia.
Bibliography:
"Iphigenia." Encyclopedia Mythica. 2013. Encyclopedia Mythica Online. 6 Oct. 2013 <http://www.pantheon.org/articles/i/iphigenia.html>.