Instagram has been a powerhouse inside of Facebook, and CEO Kevin Systrom and COO Marne Levine deserve most of the credit.

Systrom gets points for realizing Instagram’s high bar for posts was turning people off, and that Snapchat’s temporary sharing model was the way to go. Levine, who runs all of Instagram’s business, gets points for turning those products into significant moneymakers.

Facebook doesn’t break out Instagram revenue, but research firm eMarketer estimates that Instagram will do more than $4 billion in revenue this year, more than double its estimated 2016 total. And Instagram’s shameless copying of Snapchat seems to be paying off — its version of Stories, a Snapchat invention where posts disappear 24 hours after they’re shared, already has significantly more users than Snapchat’s entire app.

In fact, Instagram has become Facebook’s best weapon for fending off Snapchat — and any other apps popular with smartphone-wielding teens and Millennials threatening to leave Facebook’s orbit. That makes Systrom and Levine integral to Facebook’s future.

This article originally appeared on Recode.net.