Australia's Head of State is the Queen of Australia, Her Majesty Queen Elizabeth II. Under the Australian Constitution, executive power is exercised by the Governor‑General as the Queen's representative. The Governor-General is appointed by the Queen on the advice of the Prime Minister of Australia. The Prime Minister is Head of Government.
A biography for the Governor-General can be found on the Governor-General's website.
Each state has a governor, who is appointed by the Queen on the advice of the Premier (head of government) of that state.