Walter White (Bryan Cranston) completed his transformation into ruthless drug kingpin during season 4 of  "Breaking Bad."

Editor’s Note: This story may contain spoilers.

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The hit AMC series "Breaking Bad" returns to TV on July 15

Show pictched as "story about a man who transforms himself from Mr. Chips into Scarface"

The return will mark the final season for the series

CNN  — 

“Breaking Bad,” which returns for its fifth and final season July 15, is one of those shows that deserves to be mentioned in the same breath as “The Sopranos,” “The Wire” and “Mad Men” when discussing the greatest TV series of all time.

Last season’s explosive finale saw Walter White (Bryan Cranston), the teacher-turned-meth-maker, kill his boss, drug kingpin Gus Fring, in a horrific, jaw-dropping act that will surely go down as one of the best assassinations in TV history. The moment sets expectations incredibly high for these final 16 episodes, which will air in two parts (the final eight episodes will premiere in the summer of 2013).

When creator Vince Gilligan first pitched the show, he described it as “a story about a man who transforms himself from Mr. Chips into Scarface.” But how do you turn a straight-laced chemistry teacher into a cold-blooded crank cooker and one of TV’s most compelling characters?

After rewatching all 46 episodes, we highlight 10 key moments that show how Walter White discovered his inner Tony Montana (actually, his inner Heisenberg. More on that.).

As each moment unfolds, Walt uses twisted rationalizations to justify his actions, which grow more calculating and manipulative as the series progresses. It’s the same sort of manipulation game Gilligan and company are playing with viewers, who first feel sympathy for Walt, but by the end of the fourth season are forced to re-evaluate their loyalties.

If you’ve never watched the show and plan on catching up, consider yourself warned: What follows is an entire list of spoilers. So what caused a seemingly average family man and teacher to break bad? Let’s begin with …

1. The cancer diagnosis (Pilot, season 1)

When Walter discovers he has terminal lung cancer, he decides to cook meth to provide money for his family after he’s gone. Even though Walt has the brains, he doesn’t know squat about the drug business. When he and his partner, former student Jesse Pinkman (Aaron Paul), attempt to sell their first batch to drug dealers Krazy-8 and his cousin, Emilio, it leads to a hilarious and heart-pounding scene that opens the pilot episode and ends with …

2. Krazy-8 in the basement (“Cat’s in the Bag…” season 1)

To avoid being shot by the two dealers, Walt kills them with a chemical gas. Krazy-8 survives, Emilio doesn’t. He’ll be first of many deaths directly and indirectly connected to Walt. Because Walt doesn’t have the heart to kill Krazy-8, he keeps him trapped in the basement with a bike lock around his neck. With each passing day, Walt grows weary of killing Krazy-8, especially when he realizes that Krazy-8 may have sold him a baby crib when the dealer worked at his father’s furniture store as a teen. It’s only when Walt realizes that Krazy-8 plans to kill him with a plate shard that he gets up the nerve to choke him. Walt realizes he’s not cut out for the drug trade. But then …

3. Pride gets in the way (“Gray Matters,” season 1)

When his wife (Anna Gunn) reveals Walt’s illness to a couple of wealthy friends, they offer to pay for his treatments. But Walt can’t bring himself to accept charity. His pride will become a recurring issue throughout the series and is a major factor that drives Walt’s darker instincts, which leads to …

4. The killer alter ego (“Crazy Handful of Nothin’,” season 1)

Enter “Heisenberg,” Walt’s bolder, more cunning alter ego, who literally wears the black (pork pie) hat. Early on, Walt slips on the Heisenberg persona – the hat, black glasses, black jacket – as a way to man up when confronting some unsavory characters. But over time, Walt grows more comfortable as Heisenberg, which allows him to lie to himself and his family, which results in …

5. The “fugue” state (“Bit by a Dead Bee,” season 2)

At the start of the series, Walt is able to get by with telling little white lies to keep his family in the dark about is drug activities. But when he needs to explain an extended absence – after being kidnapped by another crazy drug dealer, Tuco Salamanca – he comes up with one of his craziest lies yet, which finds him naked in a grocery store with “amnesia.” It’s an example of the extreme lengths Walt will go to keep his misdeeds a secret, which include …

6.Letting Jane die (“Phoenix,” season 2)

Walt decides to let Jesse’s relapsed-junkie girlfriend choke on her own vomit because she knows everything and is the one person he doesn’t trust who can expose him. Her death is the best example of the ripple effect Walt’s decisions have on everyone around him, including Jane’s distraught father, an air traffic controller who accidently causes a mid-air collision between a 737 and a commuter plane, killing 167 people. Though Walt feels guilty about Jane’s death, it’s just another step in the process that allows him to grow comfortable with eliminating threats, including …

7. Running over bad guys (“Half Measures,” season 3)

To save Jesse, Walt uses his Pontiac Aztek, one of best comedic devices ever, as a battering ram to take out two drug dealers who, like Walt, work for Gus. Walt realizes it’s only a matter of time before Gus decides to get rid of him, which leads to …

8. Jesse killing Gale (“Full Measure,” season 3)

Gale, Walt’s assistant in the super lab set up by Gus, is unaware that he’s being groomed to take over so that Gus can kill Walt (Gus tells Gale that Walt is dying of cancer, which by this point is no longer true). Just as Walt is about to be killed by Gus’ henchmen, he’s able to get a message to Jesse, who does the only thing he can to save his partner. More than one, Jesse has been a victim of Walt’s bad decisions (including two very painful beatings) and killing Gale nearly sends Jesse to the brink. Because Gus has no one to run the lab, Walt gets a temporary reprieve, but he knows there’s only one thing he can do to stay safe …

9. Bring down the boss (“Face Off,” season 4)

The season finale’s title is a clever play on words that doesn’t begin to prepare viewers for Gus’ grisly demise. But as brilliant as Walt’s plan was, viewers don’t learn the full extent of how he pulled it off until the final shot, when we learn …

10. Walt poisoned a kid (“Face Off”)

That final shot – a slow zoom-in of a plant, lily of the valley, in Walt’s backyard – is the moment viewers realize it was Walt who gave berries from that plant to the son of Jesse’s new girlfriend, which sets off a chain events leading to Gus’ death. It’s the final devious deed that completes Walt’s transformation into a ruthless, cold-blooded kingpin. He has become Heisenberg.

Will we see his downfall in season 5? Watch and find out.