Snap is starting the year off strong. Its quarterly earnings blew past expectations, and while its redesign is angering some users, the change is expected to improve the app experience for everyone, with time.But life hasn't always been so great for Snapchat. CEO Evan Spiegel continues to be compared to Mark Zuckerberg and his tech giant Facebook, whose much larger products keep taking on Snapchat-esque features. Such a comparison isn't so crazy. Back in 2013, Facebook offered $1 billion to acquire Snapchat. Zuckerberg later upped the offer to $3 billion. And that's just one drama in a long saga of how Snapchat and Spiegel rose to fame.For more details on the rise of Snapchat, we spoke with the guy who wrote the book — seriously — on this week's MashTalk. Billy Gallagher is the author of "How To Turn Down A Billion Dollars: The Snapchat Story," which is out Feb. 13 and available on Amazon.Gallagher has quite the personal knowledge of the whole "Snapchat Story." He attended Stanford with Spiegel and was in the same fraternity. Back then, he covered the early days of Snapchat for TechCrunch. Gallagher later worked in venture capital, and now, he's getting his MBA from Stanford's Graduate School of Business. He also says his favorite Snapchat filter is the puppy lens.In the book, Gallagher illustrates the personality of Spiegel as a frat brother, someone who would stand back, solo cup in hand, and watch pledges push each other in shopping carts; someone who would ask those some pledges to help him with his startup; someone who later took Taylor Swift as his date to Snapchat's New Year's Eve party.A major character and story arc in the book is Reggie Brown, the classmate who suggested the idea of a disappearing messaging app. Brown later forced out of the company and sued. Spiegel and his fellow cofounder Bobby Murphy settled for $157.5 million.We chatted with Gallagher about Spiegel and Brown and what he predicts for the future of Snapchat. There wouldn't be a Snapchat without Spiegel, he said, and there may not be one in the future without him, he argued.Follow Billy Gallagher on Twitter.Follow MashTalk on Twitter, too.