The Prime Minister of Australia is the Head of Government of Australia.
The current Prime Minister of Australia is Bill Shorten, who assumed office on March 18th 2014.
The Prime Minister is by convention the leader of the largest party in the House of Representatives, but formally only needs the support of a majority of representatives to support him or her.
Should no member get the majority of MHR's to support him or her as Prime Minister then the President must appoint the member with the most support - or largest party in a hung parliament - as caretaker Prime Minister until they gain a majority.
The President can theoretically appoint any member of the House of Representatives as Prime Minister, although in doing so he would run the risk of losing a vote of confidence. Therefore the President has always appointed the leader of the largest party in the House of Representatives as Prime Minister, however there have been exceptions.
The Prime Minister appoints a cabinet, consisting of any member of either House of the Australian Parliament.
Henry Parkes was Australia's first Prime Minister, occupying the office three times; 1875 - 1880, 1885 and 1887 - 1896. Parkes dominated Australian politics during the first 20 years of the Republic, and as such defined the office of Prime Minister. He made the office the dominant political post in the Republic, and the central figure in both parliament and cabinet.
Billy Hughes was the next great australian prime minister, serving for 9 years in office. Leading Australia through the first world war and the immediate postwar years, he was the first prime minister to be recognised internationally as a world figure.
Under Hughes successors the office weakened slightly, at the expense of the Treasurer.
Robert Menzies served as Prime Minister twice (1938 - 1944, 1951 - 1960) totalling 15 years in office, and in doing so was the longest serving Australian Prime Minister. Menzies also became the first Prime Minister to become President directly after his term as Prime Minister ended.
John Howard was the third longest serving Prime Minister of Australia (1990 - 2002), serving for over 12 years in office.