By Alistair Barr and Edwin Chan

SAN FRANCISCO (Reuters) - Goofball, visionary, opportunist, maverick: Andrew Mason invites all manner of description but the one thing all agree on is that the Groupon CEO is one shrewd customer.

The music-studies major who says he started Groupon to get his business partners off his back is now the central figure in a $540 million IPO that has drawn scrutiny from regulators, harsh criticism from Silicon Valley, and occasional derision from the investment community.

Even scaled-back, it remains one of the biggest Internet IPOs in years. It could draw some interest as the first of the so-called daily deals websites to go public, but questions remain over the long-term profitability of an easily replicated model and its valuation.

The 30-year-old entrepreneur embarks next week on a roadshow to try and convey his long-term vision for the company, which after a rosy spell when it was touted as the fastest-growing company in history now grapples with no shortage of critics and cynics on Wall Street.

Expect fireworks.

"He has this image of a happy-go-lucky person, but he's a very shrewd businessman," said a senior industry executive who worked with Mason before leaving. "When people question Groupon, he takes it very personally and deeply. He's poured his life into the company."

The executive with a fondness for quirky antics -- such as posing for photos with a cat atop his head -- in past months has shown signs of being under severe strain.

He has had to contend with a growing list of new entrants to the daily deals space from Google to AT&T, in addition to nemesis LivingSocial, backed by Amazon.com Inc.

The Securities and Exchange Commission's poking into its financials forced Groupon to scrap controversial accounting metrics and recognize the costs of marketing and revenue-sharing with merchants more.

In September, Groupon lost COO Margo Georgiadis to Google Inc -- months after losing predecessor Rob Solomon.

A month before that, Mason lashed out against "insane" critics in a lengthy, rambling leaked memo that some said displayed more than a tinge of hubris.

Mason himself put it best. In a letter to potential investors that accompanied the first IPO filing, he made no bones about missteps.

"As with any business in a 30-month-old industry, the path to success will have twists and turns, moments of brilliance and other moments of sheer stupidity," he wrote.

'ENTERTAINMENT VALUE'

Mason tries hard to break stereotypes -- and isn't shy about advertising that fact.

The CEO appeared in the company's IPO roadshow video on Friday in a suit and tie, with hair parted neatly to the side - unusual garb for someone who prefers t-shirts.

His straight-laced talk was interspersed with occasional quirky moments. At one point, Mason compared Groupon to a cyborg -- a combination of human and technology.

Later, he said Groupon can't be boring because it sends deal emails to subscribers everyday and has to avoid people getting tired of the communications.

"Entertainment value is high with him," said Ryan Jacob, manager of the Jacob Internet Fund, who watched the roadshow video on Friday. "Within the Internet space we're used to a wide variety of executives, so I wouldn't disqualify him because he's a little unorthodox."

NO TYPICAL JOURNEY

Mason's meteoric rise to head of a multi-billion dollar company was no typical journey.

Instead of majoring in business or economics, Mason studied music at Northwestern University, graduating in 2003. Instead of moving to California to start his tech company, he stuck around in Chicago.

Groupon evolved from a venture called the Point, a site to improve online organizing and fund-raising. Mason dropped out of graduate school in public policy at the University of Chicago to work on that business. Before that, as a teenager, he started a business to home-deliver bagels on weekends.

Today, two-year-old Groupon boasts 30 million customers and deals with nearly 60,000 local merchants in 45 of countries, representing about 90 percent of the world's GDP, according to Chief Financial Officer Jason Child.

But Mason continues to ham it up. At this year's AllThingsD conference, he insisted organizers work with his drivers' license picture -- showing mouth agape and face contorted -- when it came time to put together event materials.

In the biographical information provided by Groupon at that conference, Mason claimed to be working on a book: "Unleash the Power Within: Self Help for Self Helpers."

His offbeat sense of humor can also land him in hot water. When Groupon ran ads that seemed to mock issues such as Chinese oppression in Tibet and the threat to rainforests, the subsequent public outcry forced it to pull the campaign.

But Mason can be deadly serious about his personal life. When Reuters reported his impending marriage to musician Jenny Gillespie and outlined a marriage gift registry calling for everything from a casserole pan to cream saucer for cats, Mason pulled the registry and -- uncharacteristically -- uttered nary a comment.

Sources had told Reuters that Mason put his nuptials first and tried to schedule the IPO around it -- a telling act for the helmsman of what may soon become a public company employing more than 10,000 people.

"There's a reluctance to be a CEO of a public company. To have regulators and investors tell you what to do," said the senior executive. "He's stubborn, but smart enough to be right most of the time."

(Editing by Bernard Orr)