What do Kim Kardashian, Bill Clinton, Oprah, and Eva Longoria have in common? They're all fans of life coach Tony Robbins.

Robbins, 57, rose to fame in the 1980s after the publication of his debut self-help book, Unlimited Power. Soon after, he began appearing on infomercials, and garnered a reputation as an inspiring motivational speaker. Through his subsequent books, as well as his audio programs and live events around the world, Robbins has reached millions of people.

What is it that makes Robbins so popular?

"His concepts are easy to understand and apply—there's no psychological lingo," says psychologist Elizabeth Lombardo, PhD, author of Better Than Perfect: 7 Strategies to Crush Your Inner Critic and Create a Life You Love." His examples and explanations make sense to the masses. And he provides inspirational energy like no other."

Robbins' messages resonate deeply with many people, including a long list of famous faces. Over the years, Robbins has reportedly coached high-profile personalities such as Bill Clinton, Oprah, Princess Diana, Nelson Mandela, Leonardo DiCaprio, Serena Williams, and Hugh Jackman, just to name a few.

"[Tony Robbins] teaches the most important lesson that every individual has to learn about living day to day, which is that you have choices in every circumstance," Bill Clinton said in a 2007 speech. "You have to make up your mind how you will respond to whatever it is that happens, as well as how you will try to make new things happen."

Serena Williams credits Robbins with helping her recover emotionally after surgery and a rough patch in her career. "After the injury—which is hard for anyone, really, coming back from major surgery—[my confidence] was at a 4," she said in a 2011 interview. "After working with Tony, I just felt amazing. I felt like I was a 10."

When the tennis star met actor Hugh Jackman, she suggested that he connect with Robbins too. "I heard many testimonials and I was like, 'This guy is extraordinary,'" says Jackman in an interview. "Then I became friends with Serena Williams and she told me firsthand about the sessions that she'd had with Tony, and how immediately after these sessions she had gone from being injured and kind of out of tennis to winning the Grand Slam of the Australian Open."

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Robbins' career took off more than 30 years ago, but his popularity shows no signs of fading. The self-help guru's seminars continue to attract thousands of attendees.

In a 2012 interview with Health, actress Eva Longoria explained what she got from one of his events: "[I]t just confirmed everything that I was already doing. You know, 'Take charge of your life!' I am. That's why I'm here! I did walk the coals. I walked over the fire. I love self-help, anything that's going to move you forward in life."

Last year, Maria Menounos told Health she has gone to the self-help guru's seminars with Julianne Hough. And just last week, the Daily Mail reported that Kim Kardashian West had nabbed "Diamond Premiere VIP" tickets (which retail for $3,000) to a Tony Robbins event in Los Angeles. She attended with husband Kanye West and sisters Khloé Kardashian, Kourtney Kardashian, and Kendall Jenner. And in true Kardashian form, the outing was heavily documented on Snapchat. Khloé shared this video of Kourtney and Kendall dancing at the event:

Why is Robbins so appealing to the A-list crowd? Experts say the level of trust Robbins has built up among Hollywood types plays a role.

"Because of his previous work with celebrities, other celebrities feel more comfortable with him," says Lombardo. "Having worked with celebrity clients, I know the level of concern in working with professionals in terms of understanding ('Will they judge me for all my wealth but [that I'm] still having problems?') and confidentiality."

And Robbins' longtime work with big names only adds to his legitimacy. "Tony built a strong self-help brand early on and he worked with (and associated himself with) successful people," says Ben Michaelis, PhD, a clinical psychologist and founder of OneMinuteDiagnosis.com. "Success begets success."

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The life coach's emphasis on conquering life challenges may also appeal to celebs who are working towards a goal, as Williams was after her surgery. "When you're a professional, when you're the best, people want to beat you more, want to bring you down even more," she said in 2011. "I had to realize that when you get on top, sometimes you have to work even harder."

And above all else, Robbins is incredibly motivating. "When you are with him, or listen to his programs, there is a sense of 'I can do this!'" says Lombardo.

The good news: you don't need to be rich and famous to draw inspiration from Robbins. Start by checking out one of his self-help books, which include Unlimited Power ($17; amazon.com), Awaken the Giant Within ($18; amazon.com), and the audiobook Unleash the Power Within ($30; amazon.com). Robbins has written financial books too, such as Money Master the Game: 7 Simple Steps to Financial Freedom ($28; amazon.com) and Unshakeable: Your Financial Freedom Playbook ($26; amazon.com). You can also listen to one of his audio programs (many are also available on Amazon), watch his 2006 TED Talk, or register for an upcoming seminar on his website, tonyrobbins.com.