Original: Sir Robert Gordon Menzies , KT , AK , CH , FAA , FRS , QC ( 20 December 1894 -- 15 May 1978 ) , Australian politician , was the 12th and longest-serving Prime Minister of Australia .
Simplified: Sir Robert Gordon Menzies ( 20 December 1894 -- 14 May 1978 ) was the twelfth Prime Minister of Australia .