“In Season Two, Jesse’s girlfriend Jane died. As it plays out, Mike comes and helps to clean up the evidence of heroin that they were both taking. The way that it was originally written was that Saul Goodman was the one who came and helped clean everything up but as it worked out Bob Odenkirk was not available for that episode. He was actually doing, I think, an episode of How I Met Your Mother. So Vince, very much at the last minute, came up with this character of Mike. My god we got so lucky that we were able to get Jonathan Banks and at that point I don’t think we realized how key that character was going to be to the show going forward. He really only showed up sort of as a fluke. Which is one of the things I love about television.”
– from Masters in Motion: A Conversation with Peter Gould
Don't Let Your Bundle Of Joy Cost You A Bundle.