The note that Jan Koum has taped to his desk in his Mountain View office says it all:

"No Ads! No Games! No Gimmicks!"

It's from Brian Acton, Koum's co-founder of the messaging service WhatsApp, which Facebook scooped up this week in a deal worth as much as $19 billion.

The jaw-dropping deal that has blown away Silicon Valley was very un-Koum-like in its high-wire audaciousness. Considered the heart and soul of the wildly popular app, the Ukrainian-born Jew who left his Communist homeland as a teenager and started his working life in America sweeping floors at a grocery store is a notoriously low-key, under-the-radar sort of entrepreneur. The mantra at his five-year-old, 55-employee startup: Mobile messaging is the medium. Don't muck it up with ads and hoopla. And above all, don't mess with users' privacy. And since WhatsApp doesn't collect personal information like names and ages, Koum's creation represents the polar opposite of the world he fled.

"It's a decidedly contrarian approach shaped by Jan's experience growing up in a communist country with a secret police," Jim Goetz, Sequoia Capital partner and Koum's venture capital backer, wrote in his blogpost, where he also mentioned the note on Koum's desk. "Jan's childhood made him appreciate communication that was not bugged or taped."

In a valley oozing with out-of-the-blue startup stories, Koum's success has been compared to that of fellow immigrants like Google's Russian-born co-founder, Sergey Brin. But Koum's journey from a small village outside Kiev to his perch among Silicon Valley's self-made billionaires has been downright spectacular.

He could not be reached for comment for this story, but according to a profile published this week in Forbes, he and his mother fled the anti-Semitism and political turbulence of his homeland when he was 16 and ended up in Mountain View, living on government assistance and squeezed into a tiny two-bedroom apartment. Koum swept floors to survive. When his mother was diagnosed with cancer, the two lived off her disability allowance.

After dropping out of San Jose State University, he landed a job at Yahoo where he spent nine years in systems security and then infrastructure engineering, and eventually met Acton. They left Yahoo in 2007, launched WhatsApp two years later, and with their users multiplying around the world to nearly half a billion today, the rest is viral history.

"We've seen these stories in the Valley over the years, whether it's garage startups like Apple and HP, or ones that come from university connections,'' says analyst Tim Bajarin with Creative Strategies. "But every so often, you get a guy like Koum that sort of comes out of nowhere. And his success really speaks to the fact that no matter what country or background you come from, there is significant opportunity here if you've got the right idea and are willing to work hard.

"And this guy,'' he says, "is a perfect example of that.''

Yahoo declined to comment. WhatsApp did not respond to a request to speak with Koum, who reportedly owns 45 percent of the company and is now personally worth billions. Relatively little is known about his personal life; Koum's Wikipedia page contains only two paragraphs. And while the Twitter page for @jankoum features a line from rapper Kanye West ("We on a galaxy the haters cannot visit'') and shows 12,000 followers, he's only following one person -- "Jesus Christ, SV.''

When Koum does talk to reporters, which is rare, he's all about the app, not the man behind it. During a conference call Wednesday with Facebook CEO Mark Zuckerberg, who said he's known the co-founder "for a couple of years'' and that he had suggested only a few days earlier that they do a deal, Koum was a man on-message, hoping to shield his social-media darling from the ravages of advertising and the money it might generate.

"Monetization is not going to be a prioritization for us," he said, referring to his goal of "making the product better, faster and more efficient. We care about details ... It's not very sexy — message speed delivery, battery life, bandwidth usage.''

Over at Facebook, which will put Koum on its board of directors, Zuckerberg claims to to share Koum's passion for openness, writing on his own Facebook page "I know that we both share the vision of making the world more open and connected.''

But on his LinkedIn page, Koum remains a man of mystery, describing himself as a senior tweet manager, and serving up only a soupçon of personal data: "barely graduated'' from Mountain View High School and "dropped out'' of San Jose State University. In his own job description, Koum writes a single line: "building cool (expletive) used by millions of people.''

One of the richest veins of information about Koum comes from his own writing on WhatsApp's blog. In rambling, sometimes humorous, prose, Koum, and presumably some of his colleagues, give readers updates on new features and ask them to celebrate milestones in their journey ("We submitted WhatsApp 2.0 into the App Store last night''). Much of it is geekspeak ("you will enjoy our use of c2dm to help you save on battery life''). Some of it is how-to tips ("if your WhatsApp is crashing all of a sudden''). Read in a single session, the stream offers an intriguing travelogue on the road Koum and Acton have followed the past five years.

Just after Christmas 2012, Koum penned what could well be the WhatsApp Manifesto -- a full-throttled tirade against advertising. Today, at the cusp of a merger with an advertising-driven Facebook, the message sounds prophetic.

"When we sat down to start our own thing together three years ago we wanted to make something that wasn't just another ad clearinghouse,'' Koum wrote. "We wanted to spend our time building a service people wanted to use because it worked and saved them money and made their lives better in a small way. We knew we could do what most people aim to do every day: avoid ads.''

"Remember,'' wrote the refugee from Ukraine, "when advertising is involved you the user are the product.''

Contact Patrick May at 408-920-5689 or follow him at Twitter.com/patmaymerc

Whatsapp co-founder and CEO Jan Koum
Born in Russia, in a village outside Kiev in Ukraine, in 1976
Moved to America in 1992
Education: Mountain View High School; San Jose State University
Previous employment: Yahoo
Source: Mercury News