US CIA World Factbook Heads of State and Government

This dataset makes the "chief of state", as labeled here, and head of government, available for all countries in the World Factbook which have such roles.

Where a monarch has a local representative of e.g. an ex-colony, both the monarch and any local representatives are generally included.

The World Factbook source pages contain much more narrative about each country. From the website:

The World Factbook provides basic intelligence on the history, people, government, economy, energy, geography, environment, communications, transportation, military, terrorism, and transnational issues for 266 world entities.