The concept of the American dream is something that makes U.S. such a special place for immigrants. No matter how harsh the reality could turn out sometimes, the United States is still the country of opportunities for many people from all over the world.

Hard work can lead to one's prosperity - and sometimes to the profit of the whole nation. According to the recent report of the Wall Street Journal,  more than 50 percent of American billion-dollar startups were founded by immigrants.

Here are three of those success stories - of the startups and the entrepreneurs - who dared to live up to their ambitions and showed once again that the American dream is worth trying.

Tesla Motors - When Dreams Lead to Luxury

The founder: Elon Musk is CEO and co-founder of Tesla Motors and he started his life in South Africa. He often claims in his public speeches that his place of birth was a violent area and that it was a challenge to live there.

Not as if his move to Canada at the age of 17 changed the latter condition - young entrepreneur had to survive on one dollar a day, while attending Queen's University in Ontario. There's a certain irony in the fact that he was the one who created a luxury company after his relocation to United States.

The startup: The total assets of Tesla Motors exceed seven billion dollars. Though Musk claims that the main future goal of the company is to offer electric cars to the average consumer at affordable prices, so far the products of this startup (electric vehicles, battery products and electric car powertrain components) are considered to be luxurious.

The potential: Elon Musk himself claims that his startup is not just about profit. "Selling an electric sports car creates an opportunity to fundamentally change the way America drives", he said.

Honest Company - When Dreams Lead to Honesty

The founder: Brian Lee came to U.S. from South Korea and originally did not intend to create any startups. He went to UCLA and was going to become a tax attorney, however, some people just cannot hold back from starting a serial entrepreneur career.

The startup: The Honest Company is worth $1.7 billion and plays a significant role on the U.S. retail market. The startup provides non-toxic household products, thus supporting the culture of ethical consumerism in the country. And though the honesty of this company has been questioned on a certain occasion, it is a good example of what a smart entrepreneur could achieve with his efforts.

The potential: according to Jessica Alba, Lee's co-founder of this eco-friendly startup, the policy of Honest Company could change the consumerism culture in U.S. "We don't test our products on animals. We test our products on our kids. And on ourselves", she said.

Cloudera - When Dreams Lead to Information

The founder: Amr Awadallah started his education as an electrical engineer back in his home country - Egypt, however, his path of a scientist and an entrepreneur took its start in United States. He became a co-founder of Cloudera startup in 2008 and now takes up a position of its Chief Technology Officer.

The startup: Cloudera's valuation is estimated to be above four billion dollars. This startup offers to its clients a Hadoop-based platform designed for data management and analytics. It offers multiple solutions to big data management and has an overwhelming potential for further growth.

The potential: "Initially", said Amr Awadallah, "We were going to build this cloud platform where we put our software on the cloud, our customers upload their data, do their number crunching and then download the results. But within six months of doing that, it was clear that all of the big banks we want to work with, the big retailers, they were not comfortable giving out their data. So we shifted company from being a cloud company to being a software company". Despite that, Cloudera's co-founder thinks that it's just a matter of time when big business will move from traditional ways of protecting and managing their data to the cloud.

These three billion-dollar startups, founded by immigrants, prove better than anything else - American dream lives on and rewards its followers.