From supermarket checkouts to convenience store shelves pretty hard to miss those shot glass size bottles labeled 5-hour energy. Tiny package promises a huge punch of pep and while only a bottle may run you 3 bucks or so, they made one man so much cash he has crooked the "forbes" billionaire list and abc's john donvan spent a day in his life. Reporter: Ten years ago the whole category didn't even exist as something you could buy, shots of energy. In the boles big and small that you seem to see for sale now here, there and everywhere. But the first one was this, 5-hour energy and the guy who came up with it, his name is manoj bhargava. And two ounces, that your idea. Yeah, that was mine. Reporter: Yeah, a $1.3 billion idea. That's what "forbes" said he was worth earlier this year. How did being outed as a billionaire change your life? Since nobody really -- not nobody but it wasn't well known before. Well, that was on purpose. I didn't want to be known, you know, people say I don't want to toil in obscurity, I like toiling in obscurity. Reporter: Obscurity gets difficult when your billion dollar product comes under official scrutiny. New york's attorney general issued subpoenas to his company and monster beverage and pepsico which makes amp seeking more details on their ingredients and how the products are marketed and advertised. Not even the trade association that represents energy drinkmakers knows the details of these subpoenas. They do, however, see little reason to worry reminding consumers of its own internal policy. Voluntarily listing total caffeine amounts on packages noting that energy drinks are not recommended for children and voluntarily not offering energy drinks for sale in k-12 schools. The issue says michael jacobson kids getting inside them what is insi inside the bottle. I don't think the average teenager thinks there are health repercussions. The caffeine causes jitters and insomnia. Mildly addictive and could cause withdrawal symptoms. Reporter: He didn't seem flustered when we talked about the cav green content and tonight he still stands by his product telling "nightline" the ag's inquiry regarding our products is routine and we do not see any material issues. Having one of those days? Reporter: For one thing he says his somewhat corny commercials are not designed to appeal to kids. He says the company doesn't market to children, period. Does the addictiveness of caffeine being sold to kids concern you? And as a dad does it concern you? Me personally for my, you know, son, no. But there is a perception out there and therefore what we do is do not market to kids. Reporter: How much caffeine is actually in a 5-hour energy shot? Bhargava says it's about what you find in a cup of premium coffee of the his view, not enough to raise a fuss about. It's overblown when it's in small contents. It's correct when it's in large quantities, but the fact that water is good, but if you have too much you drown. Reporter: In general manoj is a guy who caught himself not to get worried about too much like frills. This billionaire's office is undecorated to the point of drab. He has given away close to 90% of his money to charities in india where he lived until he was 14 when his dad moved the family to the detroit area. Good at math he got into princeton finding it pointless for him he quit after a year. You told your parents you were quitting print ton. Yeah, it didn't go over well. Reporter: I bet. I said, okay, what I'll do is I'll tell princeton I'm taking a year's leave. Reporter: So they're still waiting for you to come back. I don't think anybody is holding their breath. Reporter: For a guy who seems to take it easy he's pretty competitive. His many imitators who think it was about the bottle these were all attempts to imitate him have made almost no don't in his market share. He owns this market. What he doesn't own is fancy cars or houses. Why don't you want stuff? We were taught really to be practical. Reporter: When you were in india. Reporter: Right now that will help as what's in the bottle is a question getting the government's attention even as it sells and sells and sells. I'm john donvan for "nightline" in detroit.