Karam and his brother John have owned a menswear store in Ōtorohanga on the main street since 1965.
Ōtorohanga mayor Max Baxter said the town is still coming to grips with the loss.
"To see the two brothers side by side for so many years... this is an absolute tragedy and a huge loss for John, Karam's family, the staff in the store and Ōtorohanga," he said.
Baxter said he has already spoken with John.
"I saw John just after the news broke yesterday and at that stage you can imagine he is in a real world of hurt."
Baxter told the Herald that Karam had crossed the centre line on the highway and crashed into an oncoming truck.
He was unsure why Karam had crossed the line.
The brothers had made a huge impact on not only Ōtorohanga, but the entire country, said Baxter.
"If you're passing through Ōtorohanga, we're known somewhat for Kiwiana, we're known somewhat for the hanging baskets but we're more well known for John and Karam Haddad and the Haddad store," he said.
The brothers were also well-known for their attire – Baxter said they were always seen in their hats, with a collar or tie and a sweater or cardigan underneath a sports coat.
"They're both very much a mirror image of one another," he said.
In an online tribute, one person wrote: "They would have to be the top salesmen of the century, they were really neat when you went in-store, such a tragic loss. The world Grieves a Queen [and] Oto Grieves a King."
The crash was the second fatality in a horror day on Waikato roads yesterday.
A silver Audi collided head-on with an ambulance on State Highway 1 near Cambridge.
The driver of the Audi died at the scene and the St John ambulance driver later died in Waikato Hospital.
A nurse who was also in the ambulance was injured, but their injuries are not life-threatening, police said. They too were taken to Waikato Hospital and are in a stable condition.
A stretch of the Waikato road – labelled a "death trap" by the regional Chamber of Commerce - was closed for at least 11 hours as the site was cleared.
Waka Kotahi said safety improvements were under way for the stretch of road between Cambridge and Piarere, which covers the site of the crash.
Hato Hone St John deputy chief executive ambulance operations Dan Ohs said the long-serving ambulance officer, who worked as a patient transfer officer, had a "brave fight" after being critically injured and flown to Waikato Hospital.
However, the officer died yesterday afternoon with their family by their side.
Ohs said the St John team were "devastated" and "grieving the loss of one of our own".
Chief executive of the Waikato Chamber of Commerce Don Good called the stretch of road between Hickey Rd, where the crash happened, and Piarere a "death trap" that had claimed "an unacceptable number of lives".
"Road users, local residents and Chambers have appealed for urgent action for the right safety measures to be put in place and have been ignored."
