Paul Keating called him a "Labor rat" who should be "excommunicated". Mark Latham called him a "sell out". Julia Gillard called him her "closest confidant". A member of Bill Shorten's frontbench calls him brother.

You can call him the most powerful union boss in the country.

As national secretary of the CFMMEU - notice that extra "M", for maritime - Michael O'Connor will be head of a union with unprecedented scope and power. And he's proven, time and again, that he's not scared to wield power.

The CFMEU's Michael O'Connor. Credit:AAP

As a top CFMEU official in the 1990s he organised the loggers' blockage of Parliament House that so angered Keating. A decade later he dramatically intervened in the 2004 federal election, swinging the CFMEU behind John Howard's Tasmanian forestry policy and helping to sink Latham's bid for the top job.