This is a sculpture of the Roman goddess Bellona in the memorial's Sculpture Garden.

It was created by Bertram Mackennal (12 Jun 1863 to 10 Oct 1931), who had been moved by the Australians' actions at Gallipoli and presented it to the Commonwealth in 1920.

(Though that said, the sculpture had actually been designed in 1906. Also although Mackennal may have spent most of his life in England (from about the age of 19), he was born in Fitzroy, Melbourne in Australia.)

The tree that frames the statue has an interesting history of its own. It grew from a pine cone which had been sent to the mother of two Australian soldiers from the battleground at Lone Pine. One of her sons had died there in the battle of Lone Pine in August 1915. The other later found the pine cone on the branches that the Turks had used as cover for their trenches, and sent it to his mother. She in turn presented the resulting tree to the Memorial.

From the AWM's site:
"In Roman mythology, Bellona was the goddess of war. Throughout art history, she has been depicted with common implements of war, such as a sword or spear. Mackennal's depiction of Bellona bears the upper half of a shield, and a helmet incorporating death's head as grim evidence of the harvest of war."

The alternative name for the sculpture is simply "War".