Alongside Saul, Michael "Mike" Ehrmantraut has enjoyed plenty of screen time in the Breaking Bad universe. He has had major roles in both the original series and prequel/spinoff Better Call Saul. He also appeared briefly in the sequel movie El Camino. Thanks to his deadpan level-headedness, Mike established himself as a fan-favorite character.
Mike's character development was also quite impressive. Though he was introduced as Gus Fring's hitman and cleaner in the parent show, it was revealed in the prequel series that he used to be a Philadelphia police officer and a parking ticket booth operator at a courthouse. It's during his time as Walt and Jesse's associate that Mike made some of the show's best decisions.
Killing Leonel
As Hank was pumping up his efforts to catch the big fish, Gus became a worried man. He thus ordered the deadly cartel hitmen known as The Cousins to attack Hank. Moments before The Cousins appeared, Gus called Hank. Speaking with an electronically disguised voice, he warned him that he had a minute to save his own life.
A shootout ensued, leading to Hank getting shot four times. However, he still managed to kill one of The Cousins (Marco) and severely wound the other (Leonel). In the hospital, Leonel's room was surrounded by the DEA but Mike was smart enough to sneak in while the officers were eating chicken and deliver a lethal injection. This way, he prevented him from talking and exposing Gus.
Linking Up Saul, Walt, And Jesse With Gus
Saul was blunt when he told Walt and Jesse that they sucked at peddling meth. He suggested linking up with a big-time drug lord who'd purchase their product in bulk. Saul didn't know the drug lord personally but he claimed to know a guy who knew a guy. That's where Mike came in.
Mike was very protective over Gus but he figured that he'd have a lot to gain in the long run too if he connected his boss with gifted meth cooks. He was right in thinking this way since he ended up becoming Walt and Jesse's partner after Gus Fring's death.
Stopping Walt From Assaulting Ted
Walt was understandably infuriated when Skyler confessed she was sleeping with her boss Ted Beneke. To get revenge, Walt even tried to kiss the assistant principal but that problematic decision backfired rather badly. Walt then made his way to Beneke Fabricators to confront Ted. He not only tried smashing the windows but assaulting Ted as well.
Luckily, Mike showed up just in time to stop Walt. He twisted Walt's arms and threw him in the car to prevent him from making a fool out of himself. If Mike hadn't done this, Walt could have easily been hit with a couple of charges, including assault and damage to property.
Advising Walt Against Getting Jesse Jailed
Combo was brutally murdered while selling drugs on a rival dealer's turf, so Jesse planned to get revenge on the men behind it. Walt knew that this would create an unnecessary war so he suggested setting up Jesse and getting him arrested on a minor charge so that he wouldn't do anything stupid.
Mike advised Jesse against this course of action, reminding him that they worked for Gus, too. Gus wouldn't be too comfortable knowing that one of his associates was in jail because the authorities might just flip them and give them a deal. If Walt had gone through with his plan, Gus would have killed Jesse.
Refusing To Cooperate With The DEA
The DEA summoned Mike to their offices after Gus Fring's death since he was one of the drug lord's top employees. Mike insisted that he was the Head of Corporate Security at Los Pollos Hermanos but Hank didn't buy it.
Hank then mentioned an offshore account in the name of Mike's granddaughter Kaylee, implying that it had been seized. The DEA agent let Mike know that the $2 million in it would be released and given to Kaylee if he cooperated. Mike refused to admit that he had anything to do with the account. This was a smart move since he would have implicated himself and ended up in jail.
Rejecting Walt's Plan To Kill Gus
Walt once approached Mike at a bar and came up with the suggestion to kill Gus. Walt tried to make Mike see that they were both expendable in the eyes of Gus, hence they had to act fast.
Instead of agreeing to Walt's plan, Mike punched him in the face and left. Killing Gus was never going to be a good idea and Mike knew it. When Walt finally did it, the empire crumbled. Walt never managed to be as formidable as Gus. Instead, he was discovered and forced to go on the run.
Taking Passports Belonging To The Cartel Hitmen
Four cartel hitmen were sent to Duane Chow's warehouse to kill him but Mike showed up just in time to put a stop to things. Chow was the owner of Golden Moth Chemical, a chemical manufacturing company that supplied chemicals to Gus Fring.
After killing the hitmen, Mike took their passports. It is by analyzing them together with Gus that he realized the passports belonged to members of the Juarez Cartel. Gus thus concluded that the cartel was trying to sabotage his operations. He wouldn't have known this if Mike hadn't taken the passports with him.
Helping Jesse Clean Up Evidence
The death of Jesse's girlfriend Jane was quite devastating. Walt let her asphyxiate on her own vomit while she and Jesse had both passed out so that she'd stop influencing the young cook.
After Jane's death, Mike showed up and helped Jesse get rid of all the drug paraphernalia. If the authorities showed up and found him with drugs, he would have been arrested and this would have put a major dent in the business. As a former police officer, Mike also coached Jesse on the right words to say when questioned: "I woke up, I found her. That's all I know."
Bugging Walt's House
During one of the lowest points in their relationship, Skyler threatened to turn Walt in to authorities. Mike and Saul thus came up with the idea to bug Walt's house so that they could listen to all of Skyler's conversations. In case she called the police, they would act quickly and prevent much damage.
Mike went to the house while Skyler was away and installed all the necessary equipment. Doing so actually saved Walt's life. As Mike was leaving, he saw Walt sneaking into the house. The Cousins then showed up seconds later to kill him. To prevent the hit, Mike phoned an associate of Gus. In turn, Gus, who was unaware of what was happening, called The Cousins to call off the hit.
Uncovering Lydia's Plan
Soon after Lydia began working with Walt, Jesse, and Mike, a GPS tracking device was discovered on the exterior bottom of a barrel at the Madrigal Electromotive GmbH warehouse. Jesse informed Mike that Lydia was being tracked by the DEA and suggested they cut ties with her.
Mike doubted it since the DEA wouldn't be sloppy enough to plant a tracking device on the exterior of a barrel. He thus came to the conclusion that Lydia planted the tracking device herself in order to scare them and make them cut ties with her.