Mathias described Kumar as "like a brother" and his death as "tragic".
"He was a really, really awesome bloke. No matter how successful he was, he was really keen to give back to his village, and provide for his siblings," Mathias said.
"It's an absolute tragedy that this has happened. Things were really looking up for him."
Kumar moved from rural Ranchi, in eastern India, to Auckland in 2010.
He studied marketing at Massey University and spent several years working for security companies before starting his own business, Mathias said.
"He was the best sales rep I've ever come across. He was incredibly talented."
Most of his earnings went to his family back in India and the village he grew up in.
"Whatever wealth he made he reinvested it back in his family. He always wanted to give back and help his village in terms of getting the basic facilities. He inspired us."
Mathias recalled Kumar sending a shipment of blankets to the small town and said Kumar had also paid for his three siblings' education, as well as buying his father a car and a shop with which to earn money.
After a few years in New Zealand Kumar became engaged to a local village woman through an arranged marriage, and fell deeply in love.
He spent hours on Skype speaking to his bride-to-be, Mathias said.
About 18 months ago Kumar returned to India to wed, and was in the middle of plans to bring his wife to New Zealand when he died.
He had hoped she would be in the country before the end of the year.
His wife was devastated, as was his family, Mathias said.
Mathias is liaising with Kumar's family in India, and working to repatriate his body as quickly as possible, so family could still give their son a traditional Hindu send off.
He has started a Givealittle page to fundraise.
"I just want our community to come together to help get our boy back home to his family."
A police spokesperson said inquiries into Kumar's death were still underway.