Lydia Rodarte-Quayle was the Head of Logistics at Madrigal Electromotive in Breaking Bad, but details regarding her backstory weren't revealed until her role in Better Call Saul. The character played by Laura Fraser made her Breaking Bad debut in the second episode of season 5. Lydia went on to become one of the show's final antagonists, and an enemy in the eyes of Walter White (Bryan Cranston).
Lydia was revealed to be considerably involved in Gus Fring's (Giancarlo Esposito) dangerous dealings. After his death, Madrigal was questioned by the DEA, which worried Lydia. She later contacted Mike Ehrmantraut (Jonathan Banks) to help her get the DEA off of her back. When Mike refused, she put a hit out on him so he tried to turn the tables on her. He later spared her life and instead forced her into supplying methylamine to Walt and Jesse (Aaron Paul).
There was much distrust with Lydia's involvement in the meth business, but she managed to tip her new allies so that they could successfully perform a train heist that led to the acquisition of 1,000 gallons of methylamine. Walt worked with Lydia to expand their reach to the Czech Republic until he retired from the meth business. She then became aligned with Todd (Jesse Plemons) and the neo-nazis before they turned on her. After the fallout from her constant of lies and double-crossing, Walt ended up killing her with a poisoned packet of Stevia. But that wasn't the end of her character within the world of Breaking Bad.
Fraser reprised her role for the prequel spinoff, Better Call Saul, which gave viewers a better look into her past. In the sixth episode of season 3, Lydia was with Gus Fring as he explored the laundry facility that he intended to use as his drug lab. Los Pollos Hermanos also happened to be a subsidiary of Madrigal. Later in the season, Lydia met with Mike at the Madrigal office in Houston. After a robbery, Mike needed help cleaning the money, so Gus set it up so that Lydia would help launder it through Madrigal. The deal allowed Mike to earn $10,000 a month while acting as Madrigal's security consultant.
Lydia's role continued in season 4 of Better Call Saul as she continued to work with Mike. She asked him to stop testing the security at Madrigal, but he claimed it would look better as part of his cover story. Lydia remained at odds with Mike and complained about him to Gus. Despite Lydia's feelings, Gus remained nonchalant about the issue and told her to get Mike an official security badge.
Lydia's interactions with Mike in Better Call Saul now give more reasoning behind their tense relationship in Breaking Bad. Mike never seemed to trust Lydia and now viewers know why. Better Call Saul is returning for a fifth season in 2020 and Lydia will surely be back. The new season will surely fill in blanks centering on the partnership between Lydia, Gus, and Mike.