"[He] thinks he is the smartest guy in the room," says a well connected source whose career has crossed paths with Milne's on more than one occasion. "That is unlikely in most rooms, but given the gigs he has got he is definitely the luckiest."

Another high profile executive who has known Milne for decades describes him as "unbelievably ambitious".

"It wouldn't surprise me if he tries to do a David Hill," this person said, referring to the former executive who served as both chairman and managing director of ABC. "He has enormous self-belief"

And another person, who worked with Milne at Telstra, describes him as a "visionary" but describes his management style as "his way or no way".

Milne left Telstra in 2010, shortly after David Thodey was appointed chief executive. His profile in the corporate world subsequently dropped. Milne took on board positions at Tabcorp, and a string of smaller technology and media companies including Quickflix and Pie Networks, both of which are no longer listed.

It was Turnbull, in 2013, who gave Milne his chance to re-emerge in the upper echelons of corporate Australia. The-then communications minister appointed his former underling, and close friend, as a director of NBN Co and later the ABC.

In 2017, with Turnbull prime minister, Milne was elevated to chairman of the public broadcaster. He has defended the ABC against attacks from commercial rivals (read: News Corp) and championed an internal digitisation project known as Project Jetstream.

It was opposition to the latter, sources say,  and not the broader political noise surrounding the ABC, which ultimately sealed Guthrie's fate.

Yet Milne was unable to explain why the ABC board made that decision on Monday. "It's appalling," one source said of Guthrie's sacking, and the lack of any explanation for it. "It's not how you lead".

To some extent, the confusion reflects the unusual nature of the role.

Most media chief executives are judged on observable metrics such as TV ratings, or shareholder returns,  but the ABC communications department was on Monday unable to say what key performance indicators (KPIs) Guthrie was measured against.  The ABC's outdated charter, a document written before the internet existed, doesn't help.

"I personally think Michelle has done a good job" Milne awkwardly said in an interview with the public broadcaster's 24 hour news channel after the news of Guthrie's sacking broke. "It doesn't always work out, you know."

He knows that all too well himself.  Milne's own career has experienced its fair share of ups and downs.

Milne's tenure as ABC chair is slated to run until 2022. Governments tend to leave ABC boards alone (unlike other public bodies, such as NBN) waiting for terms to naturally expire. They do so for fear of being accused of political interference.

But with Milne's biggest supporter, Malcolm Turnbull, no longer in power, and the handling of Guthrie's departure raising eyebrows, questions will be asked about his own future.