How to wipe Galaxy 3 to give to a friend

[AC Question]

I bought a Galaxy 6 and now want to give my Galaxy 3 to a friend. I am having it unlocked by AT&T. How can I wipe just my personal data and let my friend have the phone with the other stuff when he switches to Consumer Cellular?

 

[Rukbat]

A Factory Reset will wipe everything you added since you got the phone, but a dedicated hacker could still find your data. Flashing the stock ROM (see [Samsung] How to flash Stock ROM via ODIN) would pretty much insure that there's nothing personal there.