Hansen was also an assistant to his predecessor, Graham Henry, but Foster comes into the job in very different circumstances.
The team Hansen took over had just ended New Zealand's long wait for a second World Cup triumph and boasted the talents of all-time greats Richie McCaw, Keven Mealamu, Tony Woodcock, Conrad Smith, Ma'a Nonu and Jerome Kaino.
That core group stayed on to keep the All Blacks top of the world rankings and won the Webb Ellis Cup for the third time in 2015 before all but Kaino ended their international careers.
That ultimately signalled the end of New Zealand's international dominance and the All Blacks slowly began to be reeled in by other nations from 2017 onwards.
The World Cup semi-final loss to England in Japan in October served as a stunning reminder that the rugby world is far more evenly matched than it was during the tenures of Henry and Hansen.
In the 16 years of that era, the All Blacks won 181 of 210 tests, two World Cups, 11 of 16 Rugby Championship titles and monopolised the Bledisloe Cup.
Foster knows that even as he rebuilds the team he must satisfy a New Zealand public that has become used to an extraordinary level of success.
"We need to change some things up, we're coming off a semi-final loss that hurt so there's a group with a lot of pain in it at the moment," Foster acknowledged on Wednesday.
"So how we adjust and refresh this group and change things up is going to be vital. Just to create the energy we need to get back where we want to be."
Handed a two-year contract, Foster will have to be on the lookout for fresh, young talent straight away.
Kieran Read, Ben Smith, Ryan Crotty and Sonny Bill Williams have all signalled an end to their test careers by moving abroad along with the likes of Matt Todd, Liam Squire and Waisake Naholo, who gave the All Blacks impressive depth under Hansen.
In addition, senior players Sam Whitelock, Beauden Barrett and Brodie Retallick have sabbaticals built into their contracts with the latter unavailable for the next two years while he plays club rugby in Japan.
There is also concern the 'Baby Blacks' production line that provided a stream of All Blacks until 2015 might be drying up.
After winning four straight world under-20 titles from 2008-2011 they have won only two since, with just five players in the last four years graduating to the senior side.
Given the way England and eventual world champions South Africa confronted the All Blacks up front in Japan, developing greater depth in the tight five will be seen as a priority.
Foster will also have to look at reinventing the way the All Blacks attack, with the side finding it increasingly difficult to break down defences since the British and Irish Lions tour in 2017 -- a shortcoming highlighted in the loss to England.
His association with the failed 2019 World Cup campaign as backs coach under Hansen also leaves Foster vulnerable to another problem his former boss did not have in 2012 -- a popular rival waiting in the wings.