Sam Prince is one of Australia's richest Gen Y-ers, but you wouldn't know it if you saw him walking down the street.
The 33-year-old founder of Zambrero, Australia's largest Mexican chain, is as relaxed and down-to-earth as they come, but he is a man on a mission.
Ranked 10th in last year's BRW Young Rich List, which placed his net worth at A$294 million ($318 million), Dr Prince has been on a relentless campaign to grow the business he founded as a 21-year-old medical student in 2005 with just A$17,000 ($18,400).
In the past two years, Zambrero has more than doubled its reach from 71 to 164 stores, boosting his wealth as the sole owner of the franchise company.
But it's not just money that drives him; Dr Prince decided early on that he wanted to build philanthropy into his business model.
"After completing my internship and residency, I felt guilt that my parents came from a very humble beginning, and I now owned a couple of restaurants and had become a doctor," Dr Prince told news.com.au.
He uses his platform and business profits to help the needy, funding health programs and donating a meal for every Zambrero meal sold as part of its Plate 4 Plate initiative, which has now given more than 30 million meals to people in the developing world.
A second-generation immigrant of Sri Lankan heritage, Dr Prince draws inspiration from his parents, who pulled themselves out of poverty and brought him to Australia as a young child.
His mother was the first person in her village in Sri Lanka to attend university, and she went on to become an economist at the Australian Bureau of Statistics, with five degrees and a PhD.
"I think there was a baton of kindness that was passed onto me," he said.
"I strongly believe that people shouldn't end up in the same place, that's not fair, because some people work very hard to get where they are. but I think that where we can it's important to make sure that people start from the same place.
"My mother comes from a family where her brother passed away because they couldn't afford health care and, for many years, the household income was zero when she was growing up ... [But] one thing my parents had is they had those basic human rights of education and healthcare, which helped them propel themselves forward."
But having a heartfelt mission does not guarantee success in the rough-and-tumble world of Australian retail. So how did Zambrero become such a prolific fast food presence?
One thing that helped Dr Prince stay on track was his willingness to ask more experienced entrepreneurs for advice.
"I have been very blessed by the generosity of the people who were happy to mentor me, including Nobel prize winners and very successful entrepreneurs, since I was really a punk kid," he said.
He counts some of Australia's greatest business minds as his personal mentors, having boldly reached out to his idols as a young upstart.
I think there was a baton of kindness that was passed onto me.
"Guys like Terry Snow from Canberra, who built the airport, there were a lot of local legends that I followed," Dr Prince said.
"They're not the Elon Musks or Steve Jobs of the world, and I love those guys, too, but for me they were more accessible ... I knew I could reach out and have a cup of coffee with them."
Another close mentor is fellow philanthropist Glenn Keys, the managing director of private healthcare provider Aspen Medical.
Although he died before Dr Prince could reach out to him, Crazy John's late founder John Ilhan, a Turkish immigrant who became the richest Australian under 40 in 2003, was a formative influence.
It was through devouring books by his heroes that the young Dr Prince discovered his entrepreneurial spirit in his youth.
"While I hadn't met any of those people yet, they were characters in my life; I felt like I was learning through their wisdom and their stories," he said.
It was with "reckless naivety" that he decided to go into business at just 21, he said, and through "grit, luck and some passion for the business", a single Zambrero takeaway joint in Canberra became two and then three, with the profits from each outlet funding the opening of the next.
In a free market it's innovate or perish, and I think you just need to compete on your product, frankly, and not ask to be sanctioned by a good vibe.
When the landlord agreed to chip in A$100,000 to fit out the third, he was stunned, saying: "I didn't know there was such a thing as fit-out contributions."
After this initial success, Dr Prince returned to the country of his birth to do aid work in the area where his mother had grown up, where the villagers had to contend with dengue fever and snake bites, and went on to build schools.
As well as the Zambrero chain, Dr Prince owns sit-down restaurants Mejico and Indu in Sydney, genetic testing company Life Letters and One Disease, the not-for-profit he founded which aims to eliminate preventable diseases from remote indigenous communities.
After initially focusing his overseas relief efforts on school building, he launched the Plate 4 Plate program after realising that "education doesn't have its full effect where kids have to decide whether to work and bring money back to the family".
But it wasn't until Zambrero was a few years old that it began to weave this philanthropic purpose into its marketing.
"We actually didn't even talk about it at the beginning," he said.
Although customers are informed about the Plate 4 Plate program, Zambrero does not trumpet the fact that it underwrites an entire indigenous aid organisation.
The balance was about demonstrating the brand's "personality" while allowing the food to speak for itself, Dr Prince said.
"In a free market it's innovate or perish, and I think you just need to compete on your product, frankly, and not ask to be sanctioned by a good vibe."