If you live in New York City or Chicago, you may have seen the enormous YouTube ads adorning some billboards and subway trains.

The latest YouTube channel to be featured in the campaign is SciShow, an educational program hosted by Hank Green, Michael Aranda, and Caitlin Hofmeister. The team makes six videos a week, with each video answering a question related to a scientific topic, from biology and evolution to astronomy and space travel.

But SciShow isn’t Green’s first YouTube success. He and brother John (best-selling author of “The Fault in Our Stars” and “Looking for Alaska”) started their popular “vlogbrothers” channel in 2007.

Vlogbrothers became so popular, in fact, that the YouTube team reached out to them and asked them to pitch some ideas for a new channel.

Courtesy of YouTube This ad is appearing on billboards and subway trains.

“The thing I think we did better than anyone on YouTube at that time was in-depth educational stuff. So when YouTube asked us to pitch stuff, we were full of ideas,” Hank Green said to Business Insider. “SciShow was one of the two that we pitched.”

The other idea was CrashCourse, which teaches eight different courses in a series of short videos. Both were approved by YouTube, and the Greens were given some startup funding to get the projects going, though they didn’t disclose how much money they received.

“It was the best possible situation. They gave us the money, and there was no obligation to pay it back. Our ad money went to pay back that money, but they wouldn’t have come knocking if we didn’t,” Green said. “At the time it was just the two of us, so we needed the help to kickstart things.”

SciShow and CrashCourse both now have more than two million subscribers.

It turns out the Greens aren’t the only creators to get some financial support from YouTube.

“We first made a series of investments in channels to jumpstart our creator ecosystem,” YouTube writes in a September 2014 post on its blog. “Eighty-six of those channels are now among the top 1 per cent of YouTube’s most popular, but the real sign of success was the massive global fan base our creators built.”

The company also created studios called YouTube Spaces in Los Angeles, Tokyo, London, and New York, where top creators can make use of top-notch production equipment.

“Now, we feel the time is right to make another important investment in our creators,” the blog continues. “That’s why we’ve decided to fund new content from some of our top creators, helping them not only fulfil their creative ambitions but also deliver new material to their millions of fans on YouTube.”

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