A prime minister is often an element of a parliamentary government, while constitutional republics have presidents. Their roles and degree of power differ substantially from one country to another. In constitutional monarchies, like the United Kingdom, the prime minister often assumes the role of a chief executive while the official executive—the monarch—only holds symbolic authority. In other countries, like France and Russia, the prime minister and president share power.
A prime minister acts as head of government, ensuring the passage of bills through the legislature and managing the civil service. In this respect, he is similar to a president, who is the head of his country's executive branch. Presidents, however, are normally popularly elected to their offices. A prime minister may be popularly elected at some point if he is a member of parliament, but he is either chosen by his party or by the chief executive.
The office of prime minister is an outgrowth of a monarchical government. Monarchs organized cabinets to help them govern the country, and the prime minister was the chief cabinet officer. As the authority of monarchs declined and parliaments assumed dominance in constitutional monarchies, the majority parties in legislatures began selecting prime ministers. In the modern era, the approval that monarchs give to prime ministers in such governments is merely ceremonial. Presidents, however, are generally a characteristic of constitutional republics, popular governments that develop without the monarchical element.