Co je monarch? Co je monarch? One who reigns over a state or territory, usually for life and by hereditary right, especially:A sole and absolute ruler.A sovereign, such as a king or empress, often with constitutionally limited authority: a constitutional monarch. One that commands or rules: "I am monarch of all I survey” ( William Cowper). One that surpasses others in power or preeminence: "Mont Blanc is the monarch of the mountains” ( Byron). A monarch butterfly.