Prime Minister

A prime minister is the most senior minister of cabinet in the executive branch of government in a parliamentary system. In many systems, the prime minister selects and can dismiss other members of the cabinet, and allocates posts to members within the Government. In most systems, the prime minister is the presiding member and chairman of the cabinet. In a minority of systems, notably in semi-presidential systems of government, a prime minister is the official who is appointed to manage the civil service and execute the directives of the head of state.

Doctor Who
A family of Raxacoricofallapatorian aliens known as the Slitheen family surrepticiously invaded Earth by assuming the identities of several key figures in Parliament. They murdered the Prime Minister, supplanting him with one of their own - Joseph Green, who became acting Prime Minister during a staged alien visitation that the Slitheen had previously arranged. After taking control of Parliament, the Sitheen attempted to prompt England into starting a nuclear war. The Ninth Doctor as well as his companion Rose Tyler and MP Harriet Jones thwarted the alien attack, though it did result in the destruction of 10 Downing Street. Soon after, Harriet Jones was elected as the new British Prime Minister.