The National Party would have been absolutely stuffed without Bill English's knowledge, sensitivity and reasonableness, Chester Borrows says.
The former Whanganui MP was one of many to heap praise on Mr English after he announced his resignation on Tuesday morning.
Mr English said he would be quitting as National Party leader on February 27, and would make his valedictory speech on March 1.
He will be succeeded as list MP by Maureen Pugh. The National caucus is to vote on the next leader for the party and he would not state his preferred candidate.
Mr English has been Prime Minister, Deputy Prime Minister and Finance Minister, and an MP for 27 years.
Mr Borrows said Mr English was probably the politician he has most admired, because he stayed on through the tough times.
Neither he nor National's Whanganui electorate chairman Neil Walker or committee member David Bennett were surprised by Mr English's decision to step down.
"I thought he would probably reflect during the first year and certainly plan to give his successor time to establish himself as leader well before the next election," Mr Bennett said.
Politics isn't fair, Mr Walker said, and Mr English lost the role of Prime Minister despite his party winning the most votes.
"Maybe he didn't get quite to where he wanted to go, but politics is a cruel game."
All three, and Mr English himself, considered his legacy would be a dual one: both financial and social.
New Zealand came through the global financial crisis and Canterbury earthquakes and remained prosperous under his leadership, Mr Bennett said.
"I think he was an outstanding finance minister. New Zealand avoided the global depression. He borrowed, but we still have comparatively low government debt."
The current government's extra $800 million surplus is virtually all down to Mr English, Mr Borrows said.
At the same time Mr English hoped to change social welfare provision by his social investment approach - an approach that puts funding in place for the most vulnerable in order to save on prison and welfare costs later.
"His argument wasn't just around the money. It was about the moral responsibility too," Mr Borrows said.
It was a new approach, and the social sector may never look the same again.
There's nobody quite like him in the National Party at present, Mr Borrows said.
"He is almost entirely without ego. It was never about Bill. It was always about New Zealand and the National Party."
Sometimes perceived as lacking charisma, Mr English didn't get a long stretch as Prime Minister.
"New Zealanders want political leaders to be people that they wouldn't necessarily want to come home for dinner," Mr Borrows said.
Current Whanganui MP Harete Hipango said Mr English deserved recognition and respect and wouldn't speculate on who would become the next leader.
"We are still a strong, united caucus. It's just certain that we are moving into another phase," she said.