In the Westminster System, this position, called Prime Minister or First Minister, leads the Executive Branch and Parliament. It is the de facto leader of the government and holds most official powers.

King
Duke
Head of Government
Queen

Emergence of middle class

Explanation:

In the period between 11th and 14th Century a very large number of European cities were created. This was a result of the flourishing of trade and crafts. The cities were no longer  religious but already independent cities. This led o the emergence and strengthening of the middle class - traders and craftsmen.