Who was the first Governor General of Australia?

The first Governor General was Sir Charles FitzRoy, appointed in 1851 fifty years before the Australian colonies became states and federated. This appointment was in parallel to the Port Philip District and Van Diemen's Land being separated from New South Wales under new constitutions, and their Lieutenant Governors being upgraded to Governor. So the Colonial Office thought it appropriate to appoint an overall local Crown representative for them, South Australia and Western Australia (the Moreton Bay District remained part of New South Wales until separation as Queensland in 1859).

FitzRoy was Governor of New South Wales, but also theoretically had jurisdiction over other colonies, appointed 'Governor-General in and over all our Colonies of New South Wales, Van Diemen's Land, Victoria, South Australia and Western Australia'. He didn't actually use his position as Governor General, as he did not have an Advisory Council, and he declined to be an autocrat. It was suggested to him that he use his New South Wales Advisory Council, but he also decided that it would be unfair to the other colonies to take advice from a group which was not aligned to their needs, and could be competing against them, or even actively hostile to their interests. A man of principle! He carried out a couple of ceremonial visits to Victoria and Tasmania - South Australia and Western Australia being too far to justify a visit of no real purpose.

His successor as governor of New South Wales in 1854, Sir William Denison was also appointed as the second Governor General, and similarly declined to do anything on the same grounds. The position lapsed after the colonies were granted representative government in 1855.

The first Governor General of the nation of Australia was John Hope, the Earl of Hopetoun, appointed in July 1900, six months before Federation.