Mugabe (Zimbabwe) is probably one of the best more modern examples. Pinochet, Stalin, Mao, Castro, Pol Pot and Hitler are all very well-known figures who fit the definition. As for Australian tyrants? Good luck finding a genuine one (note: that's a good thing). You're looking for a leader who is, for want of more accurate description, an evil bastard. They are generally highly repressive of the population (particularly their political opposition) and their rule is usually marked by cruelty and human rights violations. The most tyrannical thing I can think of a recent(ish) Australian leader doing is probably Menzies' attempt to ban the communist party as it violated the right to freedom of association and was oppressive of individual free will and of Menzies' own political opposition.