Walter White doesn't have a character arc. He has a character slope.
Most of the great TV dramas – The Sopranos, Deadwood, The Wire, Mad Men, Game of Thrones, Battlestar Galactica, Twin Peaks – have star characters who formed their moral codes long before the cameras started rolling, and the drama comes from watching how they use those codes to react to new challenges. Breaking Bad, which airs its final episode of the year this Sunday on AMC, is different: When mild-mannered chemistry teacher Walter White decides to secretly fund his cancer treatment by making crystal meth, he's tossing his old moral code out the window, and tossing himself off a cliff. The only question is how far he'll fall.
This list is the answer. Presented below, in chronological order from the pilot to the shocking seventh episode of Seson Five (WARNING: spoiler alerts ahead), is an updated list of Walt's lowest lows – the shots and scenes where his journey from warm-hearted family man to cold-blooded killer took its greatest leaps forward, or downward. They're the moments that made you jump off your couch or shrink back into the cushions, cover your mouth or let it hang open in shock and disbelief. They're the moments that make Walt bad, and Breaking Bad great.