BB-8 is a spherical astromech droid, 0.67 metres tall, assigned to Poe Dameron. The StarWars.com Databank calls him "a skittish but loyal astromech" and Poe's X-wing co-pilot. He was introduced in Star Wars: Episode VII The Force Awakens (2015).
He is the trilogy's inciting incident
When Poe is captured on Jakku, BB-8 escapes into the desert carrying a fragment of the map to Luke Skywalker, and is hunted across the galaxy for it. The structure is a straight restatement of R2-D2 and the Death Star plans, deliberately and without apology, and it works for the same reason: the audience trusts the droid before it trusts anyone else.
Built, not rendered
The decision to realise him as a physical, on-set puppet rather than a digital character is the single clearest statement of intent The Force Awakens made about its own aesthetics. Actors are reacting to something that is actually in the room, which is why the performances around him land.
Not just a mascot
The Databank's list of his actual accomplishments is longer than his screen time suggests: infiltrating a prison facility on Canto Bight, commandeering a scout walker aboard a First Order flagship, and befriending the droid D-O. He does more plot work than most of the human supporting cast.
Continuity
Canon only.
