"Who is ICAC?’’ former billionaire coalminer Nathan Tinkler texted his employee Darren Williams in April last year on learning that an investigator from the corruption watchdog had visited his offices.

If he did not know then, Tinkler certainly knows now. He will be one of the most watched witnesses to appear before the NSW Independent Commission Against Corruption as it continues with its sensational Operation Spicer inquiry, which is lifting the lid on the realpolitik of political donations.

A colourful witness: Nathan Tinkler. Credit:Sasha Wooley

Tinkler was due to appear and expected to answer questions about a $66,000 donation made to the shadowy company Eightbyfive, which was run out of the offices of former state Liberal resources minister Chris Hartcher. But within days the inquiry has spread to the former Labor NSW government and to current Liberal police minister Mike Gallacher, who resigned on Friday, and potentially even further.

One of the common threads is Tinkler, the Hunter Valley billionaire who once owned interests in developer Buildev, the Maules Creek coalmine and Ashton Mining and had plans to build a coal loader in Newcastle.