Better Call Saul is about to shed light on one of Breaking Bad's biggest mysteries: How did Mike (Jonathan Banks) go from Philadelphia cop to grizzled New Mexico criminal?

In Bad, he was among the show's most ruthless characters and its most endearing, thanks to his relationship with his granddaughter, Kaylee. Mike has spent most of his screen time in Saul confined to a parking attendant's booth, not displaying his full range of abilities. But that's poised to change.

Clips from Monday's episode have already revealed that Mike had a son, Matt, who died under mysterious circumstances. Banks, who earned an Emmy nomination in 2013 for Breaking Bad, says that Monday's episode helps explain why Mike is so enamored with his granddaughter, as well as why when viewers meet him in Saul, he's working as a parking attendant.

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"It's the only connection he has left to his son," Banks tells The Hollywood Reporter of Kaylee. "Whether she's in the cradle or whether she's 5 or whether she's 12, he's just desperately in love. That's his granddaughter."

In a conversation with THR, Banks also reveals how much he knew of Mike's backstory before joining Saul and weighs in on a controversial scene in his final episode of Breaking Bad, season five's "Say My Name."

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Did you ever pitch your own version of Mike's backstory to the writers?

I do recall saying years ago — when I let my granddaughter Kaylee out of the car with mylar balloons just before I go to shoot people — I said to [Breaking Bad creator] Vince [Gilligan], who was directing the episode, "Vince, that is my granddaughter. That is not my daughter." I said to him "However Mike has lost his soul, wherever Mike has gone, has something to do with his son."

Did you feel the need to have input for Saul?

The writers have their pens in their hands, and that's what it's going to be. That does not mean I play a character this long, and they've been good enough to me to give dimension and not just make me some bad guy, to not have my own backstory. I know I have my own backstory, and will continue to think about my backstory.

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How early did you know you'd get a Mike-focused episode?

I don't ask a lot of questions, and I really do trust my writers. It doesn't mean I agree with them 100 percent all the time about what the character does, but I would be foolish, I would be blind not to see what good care they have taken of the character of Mike. They love the character of Mike; I love the character of Mike.

Mike leaves his granddaughter in the park to avoid being arrested in his final Breaking Bad episode. You've said you doubted Mike would do that. Have your feelings changed at all since then?

What I do after a period of time is you accept it. The reality is, what's Mike going to do? I've got to own up to what the reality would have been. What, is Mike going to get in a shootout in the park in front of his granddaughter? The reality was there's a little girl, there are a police there, and it's a relatively safe spot. And he goes. I've accepted it over a period of time. On the day when we shot it, it was very hard for me to accept.

Stay tuned to The Live Feed following Monday's episode for a spoiler-filled post-mortem with Saul writer (and former Gilligan assistant) Gordon Smith.

Better Call Saul airs at 10 p.m. Mondays on AMC.

Email: Aaron.Couch@THR.com

Twitter: @AaronCouch