The youngest brother of Duck Dynasty's Robertson family, Jep (Short for Jeptha) was seen a few times on camera in both seasons of the series, but if you go looking for him you're most likely to find him behind the camera. In addition, some consider "brother #4" to be Alan Robertson, the oldest, who is a full-time senior church pastor and has little involvement with the show.
According to Starcasm.com, Jep is the one responsible for getting all that amazing footage posted online, which is likely what brought attention to the family from A&E, and got the Duck Dynasty series rolling.
Actually, the series has been more like a steam roller lately! The LA Times reported that the last episode pulled in a record 4,900,000 viewers! That's up from the season premiere in October 2012, which even then brought in 3,800,000 viewers.