In a parliamentary system, the Prime Minister is the head of the government, having been elected by the majority party or coalition in parliament. The term also is used informally to describe a person elected unilaterally by a monarch to serve in a substitutionary capacity (see viceroy). In governmental practice the Prime Minister does not hold absolute authority (like in the Presidential system) however the Prime Minister is considered "First among equals".
First Prime Minister
Robert Walpole is generally considered as the first prime minister. Walpole was the prime minister of Britain between 1721 - 42. The British prime ministry has served as a model for the heads of government in many Commonwealth countries, Europe and Japan.
Roles of a Prime Minister
The prime minister has appointive powers and is responsible for the government's legislative program, budget, and other policies. His or her term of office lasts until the next scheduled election or until he or she loses legislative support by losing a vote in parliament. In France and Russia, which have semipresidential systems with both a president and a prime minister, the president wields greater power but the prime minister controls the domestic legislative agenda.