May 7, 1967 - Martin Bryant

The Port Arthur massacre of April 1996 remains the deadliest mass shooting in Australian history, carried out without warning against tourists and residents at a historic convict site in Tasmania. The attack prompted the Australian government to enact sweeping gun reform legislation within weeks — among the most rapid legislative responses to a mass shooting any democratic government has undertaken. The scale of the event, and the policy changes it triggered, ensured its place as a defining moment in modern Australian history.

From Wikipedia

Martin John Bryant (born 7 May 1967) is an Australian mass murderer who shot and killed 35 people and injured 23 others in the Port Arthur massacre on 28 and 29 April 1996. He is currently serving 35 life sentences, and 1,652 years without the possibility of parole, at Risdon Prison in Hobart, Tasmania.