The concept of Indo-Pacific, to a large extent, is due to the Indian Ocean Tsunami on December 26 2004. The size and scale of the destruction led four democracies, at varying states of maturity, to try to assist multiple countries hard hit by the natural calamity. The context was logistical humanitarian supply and support. Thus, the navy of Australia, India, Japan and the United States (US) all acted in unison to make sure that the region could cushion the enormity of the destruction, with the human destitution to follow.
That said, in terms of cartography, the former Australian diplomat, Professor Rory Metcalf is of the foremost thinkers on the concept of Indo-Pacific, is that it has been around at least since 1571, a decade after the circumnavigation of the globe. The map of Indo Pacific then was sketched with rather remarkable prescience and accuracy by a Flemish cartographer.