Kevin Hart is betting that the smiley (and not-so-smiley) faces are the key to generating sales.

Earlier this month, the comedian and entrepreneur unveiled 'KevMoji,' an app lets users send stickers of his face via chat services like iMessage and Facebook Messenger. The app costs $1.99, though users can unlock extra content for $0.99.

Less than five hours after launching on September 13th, KevMoji landed the No. 1 spot on the Apple paid-app charts (as of this writing, it sits at No. 3.) Hart, for his part, has been doggedly promoting the business on social medial:

KevMoji was developed by HartBeat Productions, the entertainment company that Hart owns and operates, and by Snaps, a mobile messaging platform. The launch was timed to Apple's unveiling of the new iOS 10. A new feature included in the update allows users to send apps, stickers, and GIFs directly through iMessage for the first time.

"When we decided to make KevMoji, all I knew is that we had to do something no one else was doing," Hart said in a statement. "So here we are, literally changing the face of iMessage by creating a real experience through emojis and stickers, rather than in animation."

Snaps develops what it calls "branded" iMessage applications for about 100 clients -- including Coach, Dunkin Donuts, and Burger King -- and then tracks how many of those stickers, videos and GIFs get shared. This isn't the first time the company has landed a celebrity partner. Last year, it worked with app developer Whalerock Industries to create 'Kimoji' with Kim Kardashian-West, the reality television star and entrepreneur. (The app, which once topped the Apple app store, now sits solidly at No. 14.)

Although Snaps would not disclose how many users have downloaded KevMoji so far, it claims that its ten new apps have collectively generated 3.5 million views since it launched.

The process of developing an emoji app, according to Snaps CCO Austin Bone, is more complex than you'd imagine.

"It's not just as simple as making an emoji and putting it in the market," Bone tells Inc. "It's important to capture the essence of someone or something."

In Hart's case, the actor provided a set of images that the company then adapted for messaging. In particular, Bone says, the team worked to recreate the comedian's vast emotional range.

"Kevin is so emotive and so funny, and in many ways larger than life," he adds, noting that a face that shifts from being 'happy' to 'sad' has performed especially well. The most successful emoji apps tend to have at least one iconic image: Kardashian-West "ugly crying," say, or basketball star Stephen Curry chewing on his mouth guard in StephMoji.

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Of course, it's unclear whether or not KevMoji will continue to sell big. It's not uncommon for celebrity apps to make a splash, but ultimately face declining sales. StephMoji, for instance, grabbed the No. 1 spot on the app store when it launched in June -- on the heels of the NBA finals -- but has since slipped from the rankings altogether.

Still, Bone is bullish on the future of emoji.

"Stickers in general aren't going anywhere," says Bone. "The introduction of the iMessage app store and sticker packs in general is an indicator of that."

And with some 900 million people using iMessage every day, the opportunity for KevMoji (and Snaps) is certainly great.