Iphigenia was the daughter of Agamemnon and Clytemnestra. Agamemnon being the commander of the Achaean fleet was trying to sail to Troy which was stuck at Aulis harbour by an opposing wind. When Agamemnon consulted Calchas a prophet he informed him that because he offended Artemis he would have to sacrifice his daughter to turn to wind.
There are varying accounts as to why Agamemnon had offended Artemis. Grimal (2005) proposes that Agamemnon had boasted of being a better huntsman than Artemis. Or that he had vowed to sacrifice to her the most beautiful thing born in the year of Iphigenia's birth, which was Iphigenia. Or she was punishing him for a sin committed by his father. M&L’s notes suggest that ‘he had killed a stag sacred to the goddess’
There are varying accounts as to why Agamemnon had offended Artemis. Grimal (2005) proposes that Agamemnon had boasted of being a better huntsman than Artemis. Or that he had vowed to sacrifice to her the most beautiful thing born in the year of Iphigenia's birth, which was Iphigenia. Or she was punishing him for a sin committed by his father. M&L’s notes suggest that ‘he had killed a stag sacred to the goddess’