New Zealand coaching legend Wayne Smith was Rennie's assistant and mentor at the Chiefs, and says he is a very loyal but direct man.
"He's prepared to put himself in the gun sights of those above him to fight for what he thinks is right," Smith told the Sun-Herald.
Smith, an assistant to two of the All Blacks' World Cup winning coaches, expects Australia to become an attack orientated side under Rennie.
He described him as "relentless, unwavering, loyal."
"He'll take no prisoners, " Smith said.
"He will be relentless in his pursuit of excellence and expects all around him to be the same.
"Rens expects loyalty and trust then gives it back in spades.
"He is unwavering in his commitment to attack. Players will have to lose their conservative ideas and be open to myriad possibilities of how to use the ball in a positive and logical way.
"Even behind their own goal line, if opportunities present themselves, you'd better take them."
Smith also believes Rennie's Rarotongan heritage will play a significant part in his approach.
"Rens will want the team to connect with their past and the community, to show gratitude, to build their grit and resilience," Smith says.
"He understands the need for huge personal meaning as part of a winning mindset…he is a supporter of diversity and he stands up for his people and program if he thinks it's right."
The Sun-Herald also quotes former All Black pivot Andrew Mehrtens saying: "You don't find anyone in New Zealand who says a bad word about him.
"He stays out of the limelight, he wants to get in and do his job and do it as well as possible. He'll pull together a group of guys and put his passion into it and wants them to get a good experience out of it. He'll absolutely throw everything he can into the Wallabies.
"He's coached alongside the man I've probably got the most respect for in rugby, Wayne Smith, and Smithy can't speak more highly of the guy."
And former All Black No. 8 Murray Mexted described Rennie as "a great appointment for Australian rugby".
