When Burger King went to expand its operations into Australia, they found that the name “Burger King” had already been trademarked by a take-away food shop in Adelaide. The name “Hungry Jack’s” was based on the name of the businessman Jack Cowin who brought the business to Australia. It was chosen from a list of possible alternatives provided by the parent company and the first Hungry Jack’s opened at Innaloo, Western Australia on 18th April 1971.
Andrew Terry; Heather Forrest (2008). “Where’s the Beef? Why Burger King Is Hungry Jack’s in Australia and Other Complications in Building a Global Franchise Brand”. Northwestern Journal of International Law and Business, 2008 28 (2): pp. 171–214. ISSN 01963228
EXTRA: In later years after the name “Burger King” did become available, there was an attempt by the Burger King parent company to expand into Australia with stores competing against the Hungry Jack’s franchises. Ultimately this venture was unsuccessful after it was found to be a breach of Jack Cowin’s master franchise agreement. However all this has nothing to do with the answer to original question “Why is Burger King called Hungry Jack’s in Australia?” Answer: Because at the time they originally went to expand, the name Burger King was already taken and they had to find something else. It really is that simple.