"Knightfall" (which led into "Knightquest" and finally "KnightsEnd") was a major part of DC's big 1990s push to be more edgy and extreme following the death of Superman.
After Bane discovers Batman's secret identity, he sets out to utterly exhaust him both physically and mentally by releasing every single big bad guy from Arkham Asylum for the Caped Crusader to deal with. Batman, of course, deals with every single big bad, but when he returns home to what he assumes is the safety of Wayne Manor, he finds Bane waiting for him - and he's just too tired to defeat a giant 'roid freak in a fist fight. Thus, Bane proceeds to snap Batman's back over his enormous right knee, which paralyzes Bruce Wayne forever (fortunately, "forever" in comic books translates to approximately one year).
In a moment of desperation, Batman passes the bat-mantle to a man named Jean Paul Valley - previously the armored vigilante Azrael of the insidious cult "The Sacred Order of Saint Dumas." At first, things go fairly smoothly. Using "The System" (deep psychological brainwashing from "Dumas"), Valley builds an ostentatious armored bat-suit that would make Rob Liefeld blush and defeats Bane pretty brutally, but without killing him. However, the longer Valley "plays" Batman, the more his brainwashing takes hold and the more violent and (gulp) deadly he becomes.
Eventually, Bruce Wayne rehabilitates himself, re-dons the cowl, and - with the help of Robin and Nightwing - defeats the psychotic and armored Azrael Batman. All's well that ends well?
While "Nightfall/Knightquest/KnightsEnd" started swimmingly - the book depicting Azbats (as he's sometimes referred) taking down Bane is particularly thrilling - it suffers from a general '90s malaise and a less than satisfying conclusion.
We don't yet know how much The Dark Knight Rises will borrow from "Nightfall/Knightquest/Knightsend," but we do know from the trailers that Bane will - perhaps early on? - beat Batman senseless, and it might be a beating that takes him out of the game for a good chunk of the movie. Will Christian Bale's Batman have his back broken? It's possible, if unlikely. Will someone other than Bruce Wayne take over the bat mantle? Probably not, but there has been a lot of speculation on that front.