Ardashir I, also known as Ardashir the Unifier, was the founder of the Sasanian Empire, the last empire of ancient Iran. After defeating Artabanus IV, the last King of Kings of Parthia, on the Hormozdgan plain in 224, he overthrew the Arsacid dynasty and established the Sasanian dynasty. Afterwards, Ardashir called himself King of Kings and began conquering the land that he called Ērānšahr, the realm of the Iranians.