Over the years, I have met hundreds of company founders. But Paul English, who co-founded Kayak which he took public and sold to Priceline for $2 billion in May 2013, -- giving him an estimated net worth of $120 million, according to the New York Times -- is absolutely unique.

After that, he started an incubator called Blade which ran for about two years and since July 2015, has run Lola which operates a mobile app that "connects you instantly to a travel professional who will help you plan, book and manage travel." He's also a senior lecturer at MIT's Sloan School of Management.

As English told me in an August 10 interview, besides letting famed author Tracy Kidder spend three years following him around -- with the caveats that Kidder not write about English's divorce and not make him look better than he is -- to write his book, A Truck Full of Money -- the thing that makes English unique is his passion for helping other people through mentoring.

While English was trained as a computer scientist and got started as a coder, his skills at hiring and motivating people strike me as particularly strong. And just as he now mentors younger entrepreneurs, he found himself in search of mentorship when he started founding companies. "Earlier in my career I would look for someone who was not my boss -- maybe my boss's boss or a peer or someone outside the company. Scott Cook, who cofounded Intuit, continues to be my mentor," said English.

He gave me several examples of how mentoring helped him be a better manager. "Mentors helped me understand that when working with a cofounder, it is better to split a startup's equity 50/50 because when things get challenging you will both be highly motivated to find a solution. In managing a team, I learned that it is critical to be as transparent as possible -- letting your team know what you are excited about and what worries you. Such transparency encourages your team to try to solve the CEO's problems which leads to better ideas. In managing board members and investors, I learned that it is important to take their advice only in areas where they have expertise and to use them as a sounding board rather than going to board meetings in fear of what they will ask you to do. Finally, mentors helped me appreciate how important it is to seize every customer interaction as a learning opportunity -- so I ask Lola engineers to respond to customer support issues," he said.

English went out of his way to help me understand how mentors help entrepreneurs -- introducing me to four people who agreed to talk to me about their views on the topic.

Vinayak Ranade -- a Buffalo, New York native who spent most of his childhood in India before returning to the U.S. to earn a B.S. and M.S. in Electrical Engineering and Computer Science at MIT -- is now CEO of Drafted, a startup that helps companies hire more employees through internal and external referrals -- which is far more effective, less costly, and quicker than hiring them through headhunters.

As Ranade explained in an August 15 interview, "I was about to accept a job at a New York hedge fund when a friend suggested I meet Paul English. I contacted him by email and heard back almost immediately. 12 hours after that, I met Paul's team at Kayak. I was not particularly interested in the travel search space but after meeting Kayak's VPs of technology and engineering and its chief architect I was totally hooked. I loved everyone I met, they were insanely amazing, smart and I just wanted to be around them."

English mentored Ranade through his example and coaching -- teaching him the importance of hiring the best team. "I joined Kayak because of the people. The best teams -- because of complementary skills, diverse backgrounds, and chemistry -- win. At Kayak, I ran operations for technical recruiting and was director of mobile engineering. I started Drafted at the end of 2014 after Priceline bought Kayak. I reached out to Paul for help and found him to be way more accessible than most successful, rich, tech people," Ranade explained.

Sara Wood, now a VP of Product Management at Gap, met English through her work with his non-profit, Partners in Health. As Wood told me in an August 14 interview, "I have been getting authentic advice from Paul since 2005. He gave me advice on scaling companies; the legal obligations of an executive; and how to read the capitalization tables in a Series F fund raising to ask tighter questions. He's helped me raise money by serving as a reference for investors conducting due diligence. And he's helped me to give better performance reviews to build trust on both sides. He would write three words on a piece of paper and tell someone 'This is not on the record but here is what's expected, how you're doing, and how well am I doing in helping you get there?' He also taught me the importance of thinking and being like the customer."

Polina Raygorodskaya, is CEO of Wanderu founded in 2011, that operates an app that lets its four million monthly users find the best bus and train transportation options. Wanderu is growing three-fold a year, has raised $8 million in venture capital and employs 50 people -- up from 3 in August 2013. As she explained, "When we started Wanderu, Paul helped me to understand why branding was important and how Kayak built its brand. He also introduced me to his VP of Engineering to find out how they integrated with their partners."

David Cancel has started five companies -- including cofounding Compete which London market research firm TNS acquired in 2008 for up to $150 million. As he said, "Mentoring is a way for humans to simulate how they might act by using other people's 10, 20 or 30 years of experience to model where the might want to be in the future. Paul helped me to learn the importance of people -- particularly recruiting experienced people in areas like sales leadership and finance. By taking a long view of how I can help them achieve their career goals, I have gotten better at overcoming the challenges of hiring such people."