The big man of Australia’s advertising industry just got bigger, and we’re not talking about the size of Harold Mitchell’s waist.

Already billed as the colossus of Australian offline advertising, the owner of Mitchell & Partners is set to inflate even more with his move into the rapidly expanding world of online advertising.

In a May profile, an industry observer told Good Weekend magazine,  “‘There’s a saying in Melbourne, ‘Don’t cross the fat man.”

As Australia’s leading buyer of advertising air-time and print space, Mitchell is almost on the same media mogul footing as Rupert or the late Kerry — although he scoffs at that suggestion. According to Good Weekend, last year, Mitchell & Partners spent close to $700 million placing ads on behalf of more than 500 clients, including Woolworths, Heinz, ANZ and a clutch of car and telecommunications companies.

You only have to check the seating arrangement at Machiavelli’s (prime position) or Kerry’s funeral (next to Nick Ross, the business titan’s helicopter pilot and kidney donor) to get an idea of the size of Mitchell’s metaphorical girth.

As Jane Cadzow’s profile put it:

A word from him, and a car manufacturer will switch its multi million dollar account from one network to another. At his suggestion, a department store will promote its mid year clearance sale in a newspaper rather than on radio. Consequently, broadcasting and publishing bosses promptly return his calls.

And as Mitchell’s waist has got smaller (according to Cadzow, his close friend Kerry Stokes warned him he was going to die) thanks to a personal trainer and new diet, Mitchell & Partners’ share price has only got fatter.  Despite the diet, Mitchell seems to have no problem with the big getting bigger. On the recent cross-media legislation, he had this to say:

This is a strong Government, been in office a long time, wants to make a change, and the change is a good change to make and the fact that some of the media owners disagree, I don’t think concern the Government.

In fact, it hasn’t suited everybody. There’s some little part in there that some of the owners didn’t want, but overall it is good for Australia. It is good for diversity of media ownership and it will bring us very much into the modern world.

The media buyer made waves recently with his own cross-media deals when The SMH reported the Mitchell-Initiative buying group had negotiated upfront commitments for 2007 spanning the TV, online and print assets of PBL, Seven Network, John Fairfax and News Ltd.

Mitchell may be feared by some (a friend and former employee calls him “scary”), but he’s respected by almost everyone in the business, not least for his unflinching work ethic. Mitchell’s story is a Dickensian tale of rags to riches, without the benevolent benefactor. He’s worked his guts out since starting in the advertising business as an office boy at Melbourne agency Briggs and James, after first dropping out of school to work in the same sawmill as his father after his mother left the family for good.

Mitchell completed high school at night school before studying for an advertising diploma, was an alcoholic at 21 and a teetotaller at 23. In 76, he left a highly paid agency job to start out on his own and the rest is history. He turned the adland hierarchy on its head, stealing the power from the admen and creatives and handing it to the buyers by starting one of the first companies to focus on planning and buying media exposure.

According to Cadzow, he worked every day for more than a decade, and again reverted to the seven day working week after losing everything in the early nineties. Writes Cadzow, “even now that he has 400 employees, Mitchell never turns off his mobile phone or takes a proper holiday”.

Mitchell doesn’t have time for holidays, apart from running his business on “a need-to-know basis… and I need to know everything,” he’s president of the Museums Board of Victoria, former president of the Melbourne International Arts Festival, former chairman of the National Gallery of Australia, a director of Opera Australia and a director of CARE Australia.

While he’s been married to his wife Bevelly for 43 years, by most accounts is a generous (if demanding) boss and a caring (if preoccupied) father, as Cadzow puts it, “…if you’re a TV executive locked in negotiation with him, he has all the benevolence of a boa constrictor”.