Sun is the man to see if you want to understand the mainland's ongoing plague of migrant worker complaints. His office in Xi'an helps workers claim unpaid wages and compensation for injury. A former migrant worker himself, he has crossed the line to organize a non-governmental body to tackle the problem from the grass roots.

Grievances by migrant workers are a troubling fixture in modern China. Tens of thousands of frustrated workers have rallied and rioted nationwide, leading some analysts to see labor trouble as the Achille's heel of China's economic boom.

Premier Wen Jiabao made the issue household news when he personally took up one worker's case on a visit to the Three Gorges Dam area in 2003. A year later, he signed a State Council order on labor protection that subjects employers to fines for delaying or unfairly reducing wages.

Sun finally allows me to accompany him to Lanzhou, the capital of neighboring Gansu province. It's the biggest case he's ever worked on - involving the Gansu government allegedly owing hundreds of migrant workers 3 million yuan (HK$2.8 million) of wages for the past five years. Sun has spent months trying to crack the case.

``Local protectionism in Lanzhou is strong,'' Sun warns. His words are worth taking to heart: Lanzhou is China's wild, wild west, a place with a reputation for corruption and harboring mafia bosses. A local reporter was recently beaten up by thugs while visiting a construction company in the area that owes workers wages.

Sun brings his own clout, however. He is a star peasant, touted by the Shaanxi provincial Chinese Communist Party committee and the national media as one of the newsmakers of 2004. He's a regular guest on CCTV. Through the media, Sun welcomes the public to contact him on labor rights abuses. Even his mobile phone is open to the public. I found him by Googling his name in Chinese. Among hundreds of articles and interview transcripts on Sun, the Xi'an Evening News has published his office address and phone numbers. ``His office is always open to the underprivileged,'' the newspaper reports.

It's barely 8 o'clock on a winter morning. On a door opposite a public toilet next to the staircase, a piece of paper flapping in the cold wind reads: ``Sun Wusheng Rights Protection Studio.'' The air smells of dust and traffic fumes. Already a few men in grubby cotton coats are huddling outside the room. Sun parks his rusty bicycle in the front yard and greets the waiting crowd. ``Are you that Hong Kong journalist?'' He shakes my hand without hesitation.

He apologizes for being late: He was in Henan province last night being filmed by a local crew. He's been up since 5am preparing documents for a court case he's attending later in the morning. ``I've never been interviewed by overseas media. Why is Hong Kong interested?'' he asks.

Sun is already swamped by phone calls and workers queuing up at his desk seeking legal advice. Most of the cases are about construction companies owing wages to so-called ``peasant workers,'' in local slang rural men who work on city projects.

For years, Sun was a peasant worker himself before becoming a construction supervisor.

Since 2000, he has made his name helping fellow workers and in the process has won more than 150 cases involving unpaid wages through the civil courts. With only a junior high school education, Sun taught himself law from reading textbooks.

He started his legal war in 2000 by representing himself - and winning - in a district civil court to claim wages he was owed.

True to his peasant roots, Sun says he follows the teachings of Mao Zedong. ``Chairman Mao's revolutionary tales'' are an inspiration, he says with a smile. He reads books by Mao and about Mao to prepare for court. He shows me his bible, Secret Tales of the Long March. Behind his desk, a piece of paper features a handwritten copy of one of Mao's poems. Next to it is a list of mobile phone numbers of volunteers - a dozen local college students, journalists and law lecturers who help Sun in their spare time.

Behind a pall of cigarette smoke and steam from cups of tea, he patiently talks to each visitor about their case.

Soon, three men with a TV camera arrive from Legal TV, the electronic arm of the Beijing-based national newspaper Legal Daily. The crew has come to Xi'an to make a one-hour documentary on Sun's life. He munches on a big steamed bun in front of the camera and speaks slowly: ``I always give CCTV top priority. Do you air your shows nationally or do you just sell to local networks?''

Confident that the crew is worth his time, Sun explains the Lanzhou case to us. A few months ago, he received a tearful visit from Gong Hongwa, a member of the Gansu Provincial People's Congress who had traveled from Lanzhou after seeing him on TV.

Gong had spent the past two years using all official channels in Gansu to urge the provincial government to pay 3 million yuan owed to about 300 workers whom Gong had hired in the construction of seven bridges in the province.

Shunned by the government, chased by debt collectors and with his house sealed by the court, Gong has been living in hiding. Sun agreed to take up his case and visited Lanzhou several times to collect evidence. Now it's time to confront the officials. The media will lend him a big hand, he confesses.

``From my experience, the media is far more powerful than the courts.''

Sun calls Gong to go over his plans for the next morning. ``This time the contingent is fairly big. I have journalists from Hong Kong and Beijing,'' he tells Gong.

Integral to his job is his ability to work the media. He counters the power of local officials by using the growing presence of media in China to get his message across. He answers a phone call from CCTV. Another crew is being dispatched to Xi'an to film him. ``My travel schedule is set. I can't wait for you here. Change your air ticket to Lanzhou,'' he tells them.

A few hours later, we are on the train to Lanzhou. It's a gruelling 10-hour overnight ride but Sun is reluctant to upgrade to the sleeping car. He is used to curling up on a hard seat and his only luggage is a stack of documents and a plastic bag full of buns, steamed by his wife a week ago.

The buns are Sun's staple food and have become a trademark of his media appearances. In front of Legal TV's camera, he proudly tells of how he once spent just a little more than 13 yuan on a three-day trip in Beijing as a guest of CCTV talking about workers' rights.

Sun has reason to be frugal. As a full-time activist with no government or private funding, he charges minimal fees to workers for legal advice and court representations. Sometimes he offers the service for free if the worker is too poor, he says.

Leaving his wife and two teenage children back home in a northern Shaanxi village, Sun lives in a tiny windowless room in a shabby residential quarter in Xi'an without central heating. His bed is a thank-you present from a worker. The only cooking utensil is a huge pot from a kitchen on a construction site. He owes several months' rent on his office and, ironically, while fighting for the unpaid wages of others he still owes his staff two months' salary.

After a show-and-tell session in front of the media on the train, Sun munches on his bun and takes out a fountain pen to mark documents. He pulls out a notebook from a leather briefcase he picked up from a rubbish dump. It is his only luxury.

The well-worn pages contain a wealth of phone numbers of various government departments, courts and journalists. Sun proudly shows us that he has befriended hundreds of reporters from all over China on his journey for justice.

On the second page of the notebook is a poem that Sun wrote: ``Hardship is a beautiful school/ Disadvantage is a teacher that leads to success.''

Sun was born into hardship in a village in Fuping county, about 70 kilometres north of Xi'an, in 1959. It was the height of the Great Leap Forward. Food was scarce. Sun's mother died when he was five. As the eldest son, Sun was working in the wheatfields by the age of 13. He later joined other villagers to build roads in Shaanxi, earning 30 cents a day.

He was banned from attending senior high school because of his landlord grandparents, a policy imposed by Mao. Sun says he holds no grudges about it.

For a decade, he worked as a salesman for a cement factory run by his county. In 1995, he began to use his connections and led a dozen of his fellow villagers to work on construction projects in Xi'an.

Most projects were contracted down a chain of builders who won them by knowing somebody in government. Sun, like other workers' supervisors, was at the bottom of the food chain. But the building boom was on and there was never a shortage of work. Like millions of other rural folk taking their dreams to the cities, Sun and his men toiled on construction sites during the day and slept in shelters made of bricks and asbestos with no fans or heaters. They lived on cabbages and potatoes and steamed buns. Meat was a rare treat.

The windfall upon completion of each project was the award - Sun could earn as much as 10,000 yuan per project.

Things started to turn sour in 1999 when at least five companies that he contracted work from delayed payments to him. He appealed again and again to no avail. Just before Lunar New Year in 1999, a few desperate workers in Sun's team traveled to his village and kidnapped his 13-year-old son, bringing the boy to Xi'an and demanding that Sun pay their wages.

After single-handedly rescuing his son, Sun became outraged at the companies who put him in this plight. He even thought of blowing up the homes of the crooks who owed him money.

The turning point came when he watched a CCTV show about an old Sichuan peasant who had taught himself law and won a 10-year case through the courts.

Sun asked students in a Xi'an bookstore for tips on law books. He couldn't afford to buy them so he traveled to the bookshop every day to read, until he was expelled by the sales staff. Within a month, he started to work on his district court case. By then, he had also befriended a few students at the Northwest University of Political Science and Law.

Armed with Mao's battlefield tactics from the Long March book and boosted by a bottle of beer, Sun marched to the court in his cotton shoes. His courtroom battle was almost aborted after he argued with the judge and shook his fists at the defendant. The angry judge pushed him out of the courtroom.

Despite the brief expulsion, Sun won the case, and went on winning all the cases he brought to claim the money owed to him and his workers.

His name passed by word of mouth among desperate migrants and they flooded his tiny dormitory. Sun's stories started to appear in the local press in 2003 and quickly spread nationwide. With his journalist and law student buddies, Sun opened his ``rights protection studio'' last May.

Exposing crooks one by one, Sun says so far his team has not received any threats. After all, he has the law as a weapon and he's always on the government's side. Connections with the media is also vital. The last thing a construction company needs is media exposure which could affect its chances of winning projects.

``I admire Chairman Mao because he led a small Red Army and beat hundreds of thousands of KMT troops,'' Sun says of his mentor. ``The principle is for the weak to beat the strong. We just want to help the underprivileged to grab the money from those rich people.''

Perhaps Sun secretly sees himself as the next Mao. ``He's a jungle hero,'' says Bai Weijun, a Radio Shaanxi reporter who volunteers for Sun. ``He's very determined. We admire his individualism and his charisma. We just want to help the government. It's very romantic to help the workers.''

We spend two days in Lanzhou watching Sun force provincial government officials into admitting they owe Gong and his workers money. They promise to make payments before the Chinese New Year. We also witness Sun organizing the local media to investigate the case.

We conclude the trip over celebratory bottles of Lanzhou's Yellow River beer. Sun shows us an open letter to Premier Wen that he will take to a meeting in Beijing with central government officials. ``I hope, through this case in Lanzhou, we dig out more parasites in society,'' he reads aloud.

He has big dreams. He wants to establish a Peasant Workers' Association with his volunteers whom he calls ``hot-blooded youth.'' They plan to streamline their legal work and help the government regulate the labor market.

And Mao is always with him. Sun leads us to Lanzhou railway station for another overnight trip back to Xi'an. Walking on the icy road, Sun recites Mao's famous poem Spring of Qinyuan - Snow: ``Thousands of miles are sealed by ice and covered by snow ... All the real romantic heroes, we shall see, in the present day.''