SPOILER WARNING: This article contains spoilers for The Punisher Season 2, which is now streaming on Netflix.
Daredevil's Detective Sergeant Brett Mahoney stepped up for The Punisher Season 2. After the NYPD took over the Billy Russo case at the end of Season 1, Mahoney worked to bring the villain to justice, even when it meant butting heads with Agent Dinah Madani and Frank Castle himself. In doing so, he became critical to Season 2, continuing his climb through the Marvel Netflix ranks.
Played by Royce Johnson, Mahoney made his Marvel Netflix debut in the premiere episode of Daredevil Season 1. He grew up alongside Franklin "Foggy" Nelson and remained friends with him even as their paths diverged, with Mahoney becoming a NYPD officer and Nelson pursuing law. Because of their lifelong friendship, Mahoney would pass tips about cases to Foggy, so that the startup lawyer could build cases and credibility.
As Daredevil Season 1 progressed, it became clear that Mahoney was one of the only clean cops in his precinct; the rest had been corrupted or paid off by Wilson Fisk, the Kingpin of Hell's Kitchen. Because of this and his connection to Foggy (and Matt Murdock, by extension), Mahoney became Daredevil's confidant. This led Mahoney to make several critical arrests, up to and including Fisk -- and, in Season 2, Castle himself. Thanks to these high profile arrests, he climbed the NYPD ranks, jumping from officer to sergeant to detective sergeant.
This is where we find Mahoney when The Punisher Season 2 starts out. As detective sergeant, he is in charge of the Billy Russo case -- up to and including Russo's escape from the hospital. Naturally, his role in the Russo case brought him into consistent contact with Madani, who would pay Russo a visit every day. They developed a rather antagonistic relationship, with Madani insistent that Russo was playing them all and Mahoney firm that the NYPD would pursue justice the "right" way.
In that, Mahoney becomes more or less the moral center of the series. As the stakes and the violence escalate, Mahoney brings his fellow characters back down to Earth. Like he did on Daredevil, he represents lawful good, even as other cops give in to their baser instincts. He is the ideal version of what a law keeper should be: upstanding, righteous and loyal to his oath to protect and serve. For this reason, he butts heads with The Punisher's protagonists, who operate outside the law in order to bring justice -- and, sometimes, revenge. While he learns to bend the rules a little by the end, he maintains his position and his faith in his capability to do good as a member of the NYPD.
Further, Mahoney serves as almost a parallel to Madani. She was once in a similar place; in Season 1, she too attempted to bring a corrupt government system to heel within the confines of the law. However, that resulted in a near-death experience and a heaping helping of cynicism and suspicion. As such, Mahoney's mere inclusion in the series shows how much she has changed by proxy. However, he does get a much happier ending, despite going through a few trials of his own.
Mahoney's jump from Daredevil to The Punisher adds some complexity to his character. His time on Daredevil challenged him, but perhaps not as directly as he was in Punisher. In facing Frank Castle, he revealed his commitment to both his position and his beliefs even in the face of incredible odds. This strengthened his role as the "good cop" within the Marvel Netflix universe, while adding a dissenting voice of reason to Frank's particular vehicle for justice. In that, Punisher truly gave Brett Mahoney his due.
Available now on Netflix, The Punisher Season 2 stars Jon Bernthal as Frank Castle, Ben Barnes as Billy Russo, Amber Rose Revah as Dinah Madani, Deborah Ann Woll as Karen Page, Jason R. Moore as Curtis Hoyle, Josh Stewart as John Pilgrim, Floriana Lima as Krista Dumont and Giorgia Whigham as Amy Bendix.