For more info, you should trot off to Googleland. Basically, the cousin of Agamemnon, who was a lover of Clytemnestra while Agamemnon was off fighting in the war of Troy. He planted the idea in her head to kill him when he got back. So she did. The end.

Cousin of Agamemnon,

Wooer of Clytemnestra,

Creator of a murderess.