This is called American dream, a rags-to-riches story. Jan Koum, Co-Founder and CEO, WhatsApp Inc. is now worth $6.8 Billions. 20 years back he came as a poor migrant from Ukraine with her mother. Five years back he started WhatsApp on Feb 24 2009 with little money.
 
We are reproducing his story from Forbes.
“The Rags-To-Riches Tale Of How Jan Koum Built WhatsApp Into Facebook's New $19 Billion Baby”

Jan Koum, born and brought up in a poor family in small village of Ukraine is now worth $6.8 billion. His mother was a housewife and father was a construction manager who built hospitals and schools. His house had no electricity or hot water. At the age of 16, Koum and her mother migrated to Mountain View and got a small two bedroom apartment through government assistance. His father never made it over. After shifting to Mountain View, Koum’s mother took up babysitting and he used to swept the floor of a grocery store for their daily needs.
 
He spoke good English, but was a troublemaker at school. He disliked the casual, flighty nature of American high-school friendships. At the age of 18, he himself taught computer networking by purchasing manuals from a used book store and returning them when he was done. He than joined a hacker group called WooWoo on the Efnet internet relay chat network. He enrolled himself at San Jose State University and moonlighted at Ernst & Young as a security tester.
 
Six months later Koum interviewed at Yahoo and got a job as an infrastructure engineer. He was still at San Jose State University. Her mother died in 2000. She died from the cancer. His father died in 1997. He was all alone after his parents died, but he credits Brian Acton(Co-Founder WhatsApp and his colleague from Yahoo) for reaching him and offering him support.
 
Jan Koum and Brian Acton worked together for nine years at Yahoo and witnessed many ups and downs of the company. They finally decided to left it in September 2007 and took a year to decompress, traveling around South America and playing ultimate frisbee. After this both applied for a job at Facebook, but failed.
 
Then in January 2009, he bought an iPhone and realized that the seven-month old App Store was about to spawn a whole new industry of apps. He visited the home of Alex Fishman, a Russian friend who would invite the local Russian community to his place in West San Jose for weekly pizza and movie nights. Up to 40 people sometimes showed up. The two of them stood for hours talking about Koum’s idea for an app over tea at Fishman’s kitchen counter.
 
Koum almost immediately chose the name WhatsApp because it sounded like “what’s up,” and a week later on his birthday, Feb. 24, 2009, he incorporated WhatsApp Inc. in California. Koum spent days creating the backend code to synch his app with any phone number in the world, but Early WhatsApp kept crashing or getting stuck. The following month after a game of ultimate frisbee with Acton, Koum grudgingly admitted he should probably fold up and start looking for a job. Acton balked. “You’d be an idiot to quit now,” Acton said. “Give it a few more months”.
 
Help came from Apple when it launched push notifications in June 2009, letting developers ping users when they weren’t using an app. Jan updated WhatsApp so that each time you changed your status — “Can’t talk, I’m at the gym” — it would ping everyone in your network. The only other free texting service around at the time was BlackBerry’s BBM, but that only worked among BlackBerry’s. There was Google’s G-Talk and Skype, but WhatsApp was unique in that the login was your own phone number. Koum released WhatsApp 2.0 with a messaging component and watched his active users suddenly swell to 250,000.
 
The two were often up there, Acton scribbling notes and Koum typing. In October Acton got five ex-Yahoo friends to invest $250,000 in seed funding, and as a result was granted cofounder status and a stake. The founders occasionally switched the app from “free” to “paid” so they wouldn’t grow too fast. In Dec. 2009 they updated WhatsApp for the iPhone to send photos, and were shocked to see user growth increasing even when it had the $1 price tag.
 
By early 2011 WhatsApp was squarely in the top 20 of all apps in the U.S. App Store. Two years later in Feb. 2013, when WhatsApp’s user base had swelled to about 200 million active users and its staff to 50, Acton and Koum agreed it was time to raise some more money. They decided to hold a second funding round, in secret. Sequoia would invest another $50 million, valuing WhatsApp at $1.5 billion. At the time Acton took a screenshot of WhatsApp’s bank balance and sent it to Goetz. It read $8.257 million, still in excess of all the money they’d received years before.
 
And today, the Co-Founders, the company is in billion dollars.