Chilperic I (chĬl´pərĬk), d. 584, Frankish king of Neustria (561–84), son of Clotaire I. He feuded bitterly with his brother Sigebert I, who had inherited the E Frankish kingdom that came to be known as Austrasia. Their struggle became savage after Chilperic and his mistress and future wife, Fredegunde, murdered (567) Chilperic's second wife, Galswintha; she was the sister of Sigebert's wife, Brunhilda. In the wars between the two brothers, Sigebert overran Neustria before his death (575). Later, Chilperic was murdered, probably at the instigation of Brunhilda. The feud was inherited by Chilperic's son and successor, Clotaire II.