40 Under 40: People To Watch In 2015

Von Tobel, a former Morgan Stanley trader and Harvard Business School dropout, calls her company "Weight Watchers for money." She has built an easy-to-follow online guide and community that make managing finances easier than ever — and that is valued at almost a quarter of a billion dollars.

As founder and CEO of LearnVest, Tobel oversees a team of more than 130 people, steers the growth of the company, and even finds time to do some financial planning for customers herself. The 29-year-old authored her first book, "Financially Fearless," at the end of last year, and she made the cover of Forbes earlier this fall.

An eye-opening trip to India inspired Adam Braun, 31, to found his award-winning non-profit, Pencils of Promise. The organization builds schools in impoverished communities around the world, and so far it has broken ground on about 250 schools, providing better access to education to nearly 30,000 children who would not have had the same educational opportunities otherwise.

Students at schools built by PoP reportedly score three times higher on language literacy tests than their peers. Braun published his first book, "The Promise of a Pencil," last March; it placed No. 2 on The New York Times' bestseller list.

Venture capitalists call her "the female Elon Musk." Billie Whitehouse, 27, cofounded a fashion retailer that makes garments that have technology built into the fibers. Unlike the light-up, clunky fitness bracelets that dominate the market, Wearable Experiments' designs are subtle, washable, and interactive in entirely new ways.

Whitehouse and cofounder Ben Moir's garments include Fundawear, underwear with vibrators in them that are controlled via mobile app; Alert Shirt, an athletic jersey that imitates in real-time the sensations an athlete feels during game play; and Navigate, a blazer that vibrates in the shoulder pads to indicate which direction you should turn to reach your destination.

Catalin Voss, 19, is founder and CEO of Sension, a visual interface company seeking to revolutionize the way we learn. Voss developed a lightweight facial recognition software that can track and understand many points in a person's face, having applications both in online education and in the autism community.

Sension's groundbreaking Google Glass app allows the wearer to recognize people's facial expressions in real-time. In collaboration with the Wall Lab at Stanford University, it begins clinical trials with young people who have autism later this year.

(Victoria's) Secret is out: Journelle will be the brand to disrupt the bra and lingerie business.

Claire Chambers, 34, founded the boutique lingerie store after moving back to New York to work as a management consultant and finding an aesthetic void in the industry. Journelle sells a tastefully curated selection of garments and provides customers with compassionate, expert assistance — a service far and above what the big-box stores offer these days.

As a mechanical engineering and product design major at Stanford University, Debbie Sterling, 31, felt bothered by how few women were in her program. She became obsessed with the notion of "disrupting the pink aisle" with a toy that would introduce girls to the joy of engineering at a young age.

GoldieBlox uses books and construction sets to engage kids through the story of Goldie, a girl inventor who solves problems by building simple machines.

Less pain, less blood, less expensive. That's the basis behind 30-year-old Elizabeth Holmes' revolutionary new blood test that her startup, Theranos, created. The company can run hundreds of tests on a drop of blood quicker than could be done on vials of the stuff in older blood tests.

The company has made Holmes the youngest woman and third-youngest overall billionaire on Forbes' newly released annual ranking of the 400 richest Americans.

Emma Watson, 24, did Hermione Granger proud this year. The former "Harry Potter" child actress and now UN Women Goodwill Ambassador gave a speech at the United Nations this fall about how she saw feminism in our society — and why it was an issue for men, too.

Her speech helped launch the "HeForShe" campaign, which aims to rally a billion men and boys as advocates for ending gender inequality. And in the past few months, Watson used Twitter to denounce a politician in Turkey and to respond to the gender politics of the celebrity nude photo hack.

YouTube users are changing the way we define "celebrity," blazing a new trail in entertainment distribution. Leading the charge is Felix "PewDiePie" Kjellberg, a Swedish video game commentator who has nearly 30 million subscribers on his YouTube channel.

PewDiePie, 24, rakes in over $4 million a year in ad sales and aims to start his own network.

A successful web series turned runaway Comedy Central sitcom, "Broad City" is equal parts smarts, heart, and utter weirdness. Its creators and stars Ilana Glazer, 26, and Abbi Jacobson, 30, are being heralded by television critics as the next Lena Dunham for their honest portrayals of life as 20-something women in New York.

But "Broad City" carves a niche in the "Girls" and "2 Broke Girls" genre with its brute realism and insanity, sending a message to critics that not all "girl shows" are the same. Season 2 premieres Jan. 14.

In February, Facebook announced that it would be buying Jan Koum's international texting app WhatsApp for $19 billion in cash and stock — probably the biggest acquisition news since Yahoo bought Tumblr. And Koum, 38, who once lived on food stamps, became an overnight billionaire.

WhatsApp revolutionized mobile instant messaging for its more than 400 million monthly users — especially for users messaging one another internationally — because, unlike other messaging apps, WhatsApp will never add additional roaming charges to your phone as long as you have a strong internet connection.

Jason Collins became the first openly gay NBA player in April 2013 when he came out in a Sports Illustrated article.

During his 10-day contract with the Brooklyn Nets, Collins wore the No. 98 jersey as a tribute to college student Matthew Shepard, who was brutally murdered in 1998 because he was gay. It became the top-selling jersey at NBAStore.com, and Collins and the league donated proceeds to the Gay, Lesbian & Straight Education Network and to the Matthew Shepard Foundation.

An active member of the You Can Play and It Gets Better movements, the 35-year-old free agent continues to advocate for inclusion, and he has called for change in locker-room language as a guest speaker at NBA seminars for rookie players.

Jessica Alba, 33, and her cofounder, Christopher Gavigan (former CEO of the nonprofit Healthy Child Healthy World) started The Honest Company "to help moms and to give all children a better, safer start."

The natural and eco-friendly baby products are a godsend to sustainability-minded moms around the country and, soon, the world. The company just raised $70 million and is valued at almost $1 billion, and it is planning to expand into some Asian and European markets.

Joshua Kushner, 29, along with cofounders Kevin Nazemi, 33; and Mario Schlosser, 34; shook up the healthcare industry last year when the trio launched Oscar, an alternative insurance company that uses technology to make insurance simple, intuitive, and human.

The site is well-designed and easy to navigate, and it tries to one-up traditional companies like Aetna and UnitedHealth by making bill-paying a breeze and by allowing members to consult with doctors over the phone at no additional charge.

Hampton Creek CEO Josh Tetrick, 34, is slowly but surely making the egg obsolete. Tetrick says his product is 48% cheaper than using conventional chicken eggs, which get much of their cost from chicken feed. Hampton Creek's eggless products, which include mayonnaise and cookie dough, cut this cost out of the equation. The company received $23 million in funding in February.

Many have tried to make eggless versions of things like mayo or cookie dough but managed to make only subpar, I-can-tell-the-difference products. Tetrick's company is making both of those products, they taste good, and they're even fooling people in taste tests.

Malala Yousafzai, 17, became known around the world when she was shot by the Taliban for speaking out against their oppression of women and girls, especially when it came to education.

The teenage activist published a book, "I Am Malala," last year and was nominated for but did not receive the Nobel Peace Prize. This, however, was Yousafzai's year, making her the youngest Nobel Prize laureate in history.

Marissa Mayer made a name for herself as one of Google's original hires, climbing the ranks and becoming the company's first female vice president. As Yahoo's CEO, she overhauled its photo-sharing site Flickr, redesigned the home page, and spent more than $1 billion dollars to acquire the blogging platform Tumblr, which, it was recently revealed, Mayer plans to make Yahoo's "answer to YouTube."

Despite data that suggests teenagers in the US are tired of Facebook, the company is stronger than ever. Facebook's second-quarter earnings exceeded expectations, and its stock hit an all-time high, cementing 30-year-old Mark Zuckerberg's seat as No. 16 on Forbes' billionaires list.

Facebook also continues to come out with new features, like self-destructing posts, giving the social network a Snapchat-esque quality. He also took a big gamble on virtual reality when he bought Oculus VR in March, and he is working on a passion project known as Internet.org, with which he plans to make the web available world-wide through the use of droids and satellites.

Clearpath Robotics uses robots to complete some of the dirtiest jobs in the world — essentially, jobs that are dangerous for people to do. Clearpath Robotics robots are being used to collect samples and clear waste, among other hazardous tasks. But rather than take jobs from humans, the robots are freeing up these employees to do less-dangerous work.

Founded by CEO Matt Rendall, CTO Ryan Gariepy, and COO Bryan Webb (along with a fourth cofounder who is no longer active in the company), Clearpath Robotics has also joined the fight against "killer robots" — that is, while Clearpath fully supports automated robots, it does not condone the use of robots as automated weapons.

The former mayor of Florence took the big seat in Italy's government in February, becoming the youngest prime minister of the country since Benito Mussolini.

Since taking office, Renzi, 39, has already passed a 2015 budget that will cut taxes by 18 billion euros ($23 billion) — the largest in Italian history. He has also been proactive in foreign affairs, meeting with numerous powerful world leaders including German Chancellor Angela Merkel and US President Barack Obama.

Since its IPO in June, GoPro has seen an incredible increase in the value of its shares, which have no intention of slowing down.

Founder Nick Woodman, 38, started making GoPro cameras, created to take extreme action shots, in 2002. The former surfer designed the camera to be light, portable and affordable and to take great, high-res photos and videos. Unlike other cameras of its kind, the GoPro products don't compromise their wearers in terms of movability or quality of footage.

HBO's thriller cop drama "True Detective" captured five Emmy Awards, a second season, and 10.9 million viewers on average each week. Critics heralded the series for its innovative format: shattering buddy cop clichés, using unreliable narrators, and inserting postmodern literary devices in a mainstream television show.

Creator Nic Pizzolatto single-handedly wrote the series one script, a feat almost unheard of, and director Cary Fukunaga won an Emmy for episode four's six-minute tracking shot, hailed as "the most incredible TV moment for years."

Season 2, which has already stirred tons of casting buzz, premieres summer 2015.

TED senior fellow Nina Tandon, 35, is pioneering research that would allow patients to regenerate broken bones or create bone implants using their own stem cells.

Her startup, EpiBone, uses technology that can provide a better bone graft that will provide exact defect repair, simplify surgical procedures, and shorten recovery times. And because the bone is made from the patient's cells, there is no chance of rejection.

This year, 21-year-old college dropout Palmer Luckey sold his virtual reality startup, Oculus VR, to Facebook for $2 billion.

How exactly Mark Zuckerberg will integrate fully immersive virtual reality into the social network experience isn't known. But the Oculus Rift headset is poised to revolutionize online "hangouts," address larger societal issues (like being used as a treatment for soldiers with PTSD), and change the way we consume video games, music, movies, TV, sports, and more.

This year, Stanford dropout Sam Altman took the reins at Y Combinator, an accelerator that has provided seed funding and guidance to emerging startups like Dropbox and Airbnb. His first batch as president included the incubator's first biotech and nuclear fusion companies, among others working on solutions to global problems.

The 29-year-old also launched an "open source" startup class at Stanford, in which Silicon Valley bigwigs Marc Andreessen, Marissa Mayer, and Peter Thiel act as guest lecturers. All presentations, readings, and assignments are available on Altman's website.

After securing a $40 million round of funding in January, the crowdfunding site Indiegogo just raised another undisclosed amount from high-profile tech notables like Virgin founder Richard Branson, Google X's Megan Smith, and PayPal cofounder Max Levchin.

CEO Slava Rubin, 36, said that one of the reasons investors get behind the Kickstarter rival is because Indiegogo allows crowdfunders to send many more international payments than Kickstarter, which can send payments to only the US, UK, Australia, New Zealand, and the Netherlands.

Amoruso had never worked in fashion before Nasty Gal — she was just a well-dressed young woman with an eye for fashion. But the 30-year-old took her eBay store and grew it, at an unbelievable rate, into a $100 million business.

The rebellious, tattooed CEO just came out with her first book, "#GIRLBOSS," this year — a less corporate, more punk-rock version of Sheryl Sandberg's "Lean In."

Ted Bailey, 32, started a software service that searches for patterns on Twitter that journalists can set up and customize for their beats. That was how CNN was first to find out about an attempted robbery investigation being pursued against Justin Bieber earlier this year.

Dataminr also offers analytics around who broke news first and the progression of its spread around Twitter. It's a revolutionary tool that will give journalists, and news consumers, the ability to get information faster and more efficiently.

When it comes to stock status, Wall Street hangs on 38-year-old Tom Farley's every word. Farley stepped into the role of president of the New York Stock Exchange in May with a lot of experience under his belt already — this is his third time as president of a global regulated exchange in three different asset classes. He fully plans to use his experience at the NYSE, he told CNBC.

Farley, who had previously been the COO of the NYSE, succeeded Duncan Niederauer, who had served as president for the past seven years.

Uber cofounder and CEO Travis Kalanick, 38, is prone to trash-talking and tantrums, but his unhinged confidence and competitiveness are part of what makes him such a brilliant entrepreneur.

His disruptive car service company was valued at $18 billion in June and operates in 128 cities across 45 countries.

Tristan Walker, 30, is solving daily shaving problems for African-American men, who are more prone to skin irritation and ingrown hair. So he started the health and beauty company Walker & Company and its first brand, Bevel, which produces high-end shaving products that reduce the razor burn and ingrowns that often come with having course facial hair.

What's more, he is building the company from Silicon Valley; only 1% of VC-backed founders are black, and Walker has already acquired $2.4 million in investments from some of the most prominent venture capital firms in the startup space.

Yao Chen is arguably one of the most powerful people in China. She has more followers on Weibo (China's version of Twitter) than the UK does residents. And she's using that power to inspire her followers to support some worthy causes. The Telegraph likens Chen to Angelina Jolie in many ways.

Like how the 35-year-old is the United Nations' Goodwill Ambassador in China, a role she accepted because she was inspired by Jolie's work. Chen is outspoken on many issues in China, like pollution and censorship, and she is involved in numerous humanitarian activities, using her wide reach on social media to promote social causes.

At a time when social-media users spent loads of time saving, editing, and deciding how to share photos, Evan Spiegel and Bobby Murphy "questioned that entire process and created something radical," Jack Dorsey writes.

Snapchat, the photo-messaging app that makes images disappear after being viewed, is valued at $10 billion and is blasting toward a mega-IPO. Among 18-year-olds, it is used more than voice calls for frequent communication with family and friends.

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