3 stars.

At one point, the doughnut chain of entrepreneur Bun Tek "Ted" Ngoy in West Coast USA was more than 75 per cent-owned by Cambodian refugees just like him. In fact, he had sponsored many of them to enter the business by getting their own franchise for selling two donuts and a cup of coffee to Californians to help kickstart their day.

It was remarkable. Once he was US-based, Ngoy helped transform the lives of Cambodian refugees by paving the way for them to set up their own doughnut shops and become a success just like him. During the late 1970s, tens of thousands of Cambodians in flight from the evil Khmer Rouge regime in their homeland were desperate for a new life in a land of opportunity. How strange it must have been for many whom Ngoy helped set up to realise that many of their customers had no idea about where Cambodia was.

This documentary is directed by Alice Gu, originally a cinematographer, who co-wrote, produced and handled the camera here. As the daughter of Chinese immigrants, she is well placed to tell the story of a Cambodian refugee of Chinese ethnicity who did good in his adopted home until his good fortune ended abruptly. In the mid-1980s Ngoy was a rags-to-riches story in the media, until a gambling obsession overtook him and the tagline reversed to "riches to rags". The Donut King documents this rise and fall.

The backstory in Cambodia during the Khmer Rouge years, related in a substantial amount of archival footage, is a reminder of the tragic history that backgrounds this story of a multi-million-dollar empire built on American's favourite pastry. The animated sequences by Andrew Hem that also progress these parts of the narrative help deflect a sombre mood that is unavoidably engendered by recounting the Cambodian experience.

Ngoy managed to escape just as Phnom Penh was falling and brought his wife, Suganthini, and their three children to America in the mid-1970s. The family were among the many tens of thousands of Cambodian refugees flown to the US.

Former army major Ngoy tried his hand at various jobs, including gas attendant, until he was drawn into a doughnut store by a delicious aroma. His favourite doughnut remains the glazed variety. He subsequently joined a three-month management training program at Winchell's, which was the top Californian doughnut business at the time.

When the Ngoys acquired their own franchise, they funnelled all their energy, and that of their three children, into the business that offered doughtnuts 24/7. Interviews with the Ngoys' grown-up children testify to the tough regime of 18 to 20 hour days, seven days a week. Dunkin' Donuts, on the other side of the country, gave up trying to enter the West Coast market, once Ngoy's business was roaring along.

I've never really got doughtnuts, myself. If you feel the same way, there is plenty of interview material that throws light on the doughnut craze, particularly from food and culture commentator Greg Nichols.

Bun Tek and Suganthini changed their names to Ted and Christy, then Ted received a reward that was presented by the president in person. Gerald Ford, seen affirming that America is built on the efforts of its immigrants, was a great advocate for America accepting refugees but the Democrat governor of California of the time wasn't quite so happy.

It is sad to see Ted Ngoy, now 77, has become a chastened man, reminiscing now he was drawn to doughnuts because they reminded him of Cambodian nom kong all those years ago. It wasn't long after he had reached giddy heights that he began to reverse his fortunes drastically.

At least he can relate with pride how he sponsored more than 100 Cambodian families to the US, and though there are some mixed feelings in his own community about him now, his story is a powerful example of how immigrants have helped shape the US. As they have Australia.

The Donut King is replete with lively, energetic characters and important social history, but I think the filmmaker could have drawn from her material more insight into the American Dream.