Dorsal view of the specimen. Those scale divisions are centimetres. Photo by Steve Jackson.
It is a female Haploscapanes barbarossa, a large rhinoceros beetle of the subfamily Dynastinae of the family Scarabaeidae.This one measured 52 mm long and weighed 62 grams. Males bear a horn on their head (hence the common name rhinoceros beetle) which they use for fighting each other, presumably over mates and territory.
Normally one would expect such a giant insect to be an inhabitant of moist tropical habitats, if not tropical rainforest and jungles. An indeed H. barbarossa is an inhabitant of the wet tropics of Australia, however in an unusual biogeographic twist the range extends not only across the drier parts of the top end but southwards in the Northern Territory, penetrating the arid country of the Tanami.
H. barbarossa has two other claims to fame: it is, according to some sources, the heaviest Australian beetle (I do wonder about this, there are some pretty enormous cerambycids) and it was the first Australian insect to receive a scientific name (by Fabricius in 1775).