"They never cease to amaze me with what they’re able to come up with, you know? I said, 'How are you ever gonna top R2-D2, the most adorable droid in movie history?'" ―Mark Hamill on BB-8

Once again dont know mutch other then what we know from lego is that he is Poe deamon's droid co-piloting his X-wing and that he was on tatooine at one point in the trailer. More info might have spoilers http://starwars.wikia.com/wiki/BB-8

This works exactly the same as paperboy's (i mean MAN's) wheatley

PS no spoilers in comments

PS big thx for aleinliomo (did i spell that right) for the photo