the person who is head of state (in several countries)

a leader of the party sustaining the majority of seats in the House of Commons and is formally appointed by the monarch

a legislator who serves as the head of a state 's government

a monarch in the relevant sense, appointed by a 'monarch' (so called - the Queen does not rule) or by the monarch's representative, holding office while he or she enjoys the confidence of Parliament

a politician who serves as the head of the executive branch of government in a parliamentary system

Leader of the government of England, post currently held by Tony Blair

in England, the head of the government; it's always the leader of whichever political party has the most seats in the House of Commons.

After the federal election, the leader of the party with the greatest number of elected candidates becomes the Prime Minister.

The Leader of the Government, who is ordinarily the leader of the party having the greatest number of seats in the House of Commons. Appointed by the Governor General, the Prime Minister selects the other members of the Cabinet and, along with them, is responsible to the House for the administration of public affairs.

The head of Canada's political executive, and usually the leader of the political party with the most representatives elected to the House of Commons.

the chief minister who leads the government

the head of the Muggle government in Great Britain (HBP1, 2)

The title given to the leader of the government formed from the party that has gained the majority of seats in the house of representatives

the Minister in charge of the Federal Government

A prime minister is the most senior minister of a cabinet in the executive branch of government in a parliamentary system. They are usually, but need not always be, a politician. In many systems the Prime Minister selects and can dismiss other members of the cabinet, and allocates posts to members within the Government.