The Great Cthulhu was the only Old One not accounted for in the Restorationist War.
Many suspected that Cthulhu had retreated to the frozen wastelands of Antarctica (another region that humanity had only recently discovered).
However, events in Australia were to prove to the contrary. With his giant octopus-like head and humanoid stature, Cthulhu is the Old One most feared by the settlers of Australia.
These were, and continue to be, the builders of the Old Ones.
They are also fearsome creatures in their own right, a nightmarish amoeba-like being with no defined form. One could say they were made from the very fabric of madness.
Although not as massive as Cthulhu or Shoggoths, Mi-go are still a terrible enemy to confront. Around the size of a human, they look like crustaceans with wings. They can fly through space, travelling between the worlds of the cosmos.
Although flying in our atmosphere is harder for them, it still allows them to move quickly, taking settlers by surprise.
The Old Ones required additional laborers when constructing their great temples and bases in the outback of Australia. Over the years they shipped re-animated humans (hence 'zombies') to these desert lands to be their servants.
Now that humanity has reached the shores of this great continent, these creatures have been let loose to create havoc and destruction. You must be careful to make sure a Zombie is thoroughly destroyed, as they have the power to regenerate.
Many humans fought for the Old Ones, for reasons psychologists are still trying to understand. It is safe to say that some people preferred their old bosses to the human usurpers.
After the war, many surviving Loyalists made their way to Australia to continue the struggle.
The Old Ones are a spacefaring race, having the ability to move between dimensions. Their temples are portals between these different worlds.
Where possible, a temple should be destroyed before something terrible can enter through the mysterious gateway.
There are places in Australia that just feel wrong, but upon investigation turn out to be devoid of any Old Ones.