Please answer a question about the following article about Liberal Party of Australia:

The contemporary Liberal Party generally advocates economic liberalism (see New Right). Historically, the party has supported a higher degree of economic protectionism and interventionism than it has in recent decades. However, from its foundation the party has identified itself as anti-socialist. Strong opposition to socialism and communism in Australia and abroad was one of its founding principles. The party's founder and longest-serving leader Robert Menzies envisaged that Australia's middle class would form its main constituency.

Who was the Liberal Party of Australia's longest-serving leader?
Robert Menzies