I wonder if this is Xylotrupes gideon, also known as the Fighting Beetle because it is used in staged beetle fights in Asia. An alternative scientific name for the same species is Xylotrupes ulysses.
The species is known to occur in eastern and northern Australia.
This guy was about 5 cm long. I found it moving hurredly across my backyard before it buried itself in soil, seeking shelter perhaps from predators or from the hot sun.
Here, it has momentarily got caught on an exposed root, keeping it still for just long enough for a photo.