Sir Robert Menzies was an Australian politician who served as the Prime Minister of Australia for a total of 18 years, making him the longest-serving Prime Minister in Australian history. He was a member of the conservative Liberal Party and played a significant role in shaping Australian politics during the mid-20th century. Menzies was known for his strong leadership and advocacy for free market economics, as well as his support for the United States during the Cold War. He was also instrumental in the development of Australia's foreign policy and played a key role in the formation of the ANZUS treaty. Sir Robert Menzies is widely regarded as one of Australia's most influential and respected political figures.