There were originally Australoids in Australia of course, but no one knows what they looked like. The may have looked like Negritos. The first Whites to Australia had stories about Aborigines waging wars of extermination on very small and very dark people whose description looks a lot like Negritos. The original Aborigines may have looked like either Negritos, Papuans or Melanesians. Papuans have an Australoid line going back a long ways. The Melanesian line goes back 40,000 YBP and is incredibly diverse.
Most modern Aborigines are a mixture of Murrayans who came out of Thailand ~17,000 YBP and went to Australia, the Philippines and eventually to Japan 13,000 YBP. This was a Veddoid type group that eventually became the Ainu in Japan. Yet another group was known as Carpinterians. They came from India 13,000 YBP. Some of the more primitive looking tribals or even possibly Tamils may be related to this group, as they do look something like modern Aborigines.
The modern day Aborigines are a mixture between Carpinterians and Murrayans.