Warning! Spoilers ahead for Supergirl's season 6 premiere.
Supergirl season 6 introduced the latest superhero tasked with protecting National City in the wake of the titular hero’s absence. At the end of the season 6 premiere episode, called “Rebirth,” Lex Luthor managed to successfully send Supergirl to the Phantom Zone, the Kryptonian space prison. In her place, Kara’s sister Alex Danvers was bestowed with a new superhero mantle: Sentinel. However, Alex’s new title isn’t a random name, it has a rich history and a deep connection to the Martian Manhunter.
Supergirl is gone, at least temporarily, trapped in the Phantom Zone until her allies can figure out a way to break her out of there. The Super Friends made a brief attempt to retrieve Kara immediately after her disappearance, but the fact they didn’t know exactly where she was located within the Phantom Zone prevented them from finding her. It’s unclear how long it will take to find the Girl of Steel. In the interim, however, Alex (donning powder blue eyeshadow in lieu of a traditional superhero mask) and the Martian Manhunter vowed to protect National City in Supergirl’s absence.
In Supergirl season 5, Alex was given a Martian watch, called the Hand of the Soldier, that allowed her to bring any weapon she wanted into existence. After leaving the DEO, Alex began her own vigilante journey, joining Supergirl in a different capacity in the field. In season 6’s “Rebirth,” Alex officially takes the next step in becoming a full-fledged superhero by getting an official moniker. The name Sentinel has a deep meaning and story behind it. Here’s who Sentinel was and why Martian Manhunter passed down the honorable name to Alex as she stepped into her role as National City’s new hero.
Alex's Sentinel Role Explained
In addition to being worried about Kara being inside the Phantom Zone and in danger, Alex is also left to wonder how the city will be protected while she’s not around. With Supergirl now unable to defend National City, Martian Manhunter believed he and Alex were up for the challenge of filling in to become Supergirl's official replacements for the time being. During their heart-to-heart in Supergirl’s season 6 premiere, Martian Manhunter tells Alex that, although she isn’t her sister, she’s still “every part a hero as she is” and that he’s seen that everyday. He also saw it when Alex summoned the strength to take down Lex Luthor, stripping him of his newfound powers and immortality.
J’onn confirms the former DEO agent reminds him of an old Martian colleague who went by the name Sentinel. She used to protect and guard with courage, thus passing down Sentinel's name for Alex to use, adding her symbol to the Arrowverse's Justice League roster. In a way, Alex is carrying on the legacy and meaning of the Martian’s former title and it’s a nice touch that it’s J’onn who gives her the superhero moniker. He’s always been one of Alex’s most ardent supporters and the pair have an incredible bond that is familial and full of love and respect. In this vein, the moment is made even better because of the connection to Martian Manhunter and his past. Alex is nothing if not committed to the cause and will surely honor her new moniker and Supergirl's vacant role in one fell swoop.
Of course, Supergirl, like all other Arrowverse shows, has employed comics lore as it befits the show and its characters. And so, Sentinel isn't the moniker of a Martian in DC Comics. Rather, the title of Sentinel has been most closely associated with Alan Scott, the first Green Lantern. When Alan returned to the comics in the 90s, he took on the alias Sentinel after losing his Green Lantern ring. The name was also adapted briefly to differentiate between him and Hal Jordan, another (and more popular) Green Lantern, before resuming his original mantle. Supergirl doesn’t reference Alan Scott’s iteration of Sentinel, which is fine since the connection to Martian Manhunter makes a lot more sense in this instance.
What Sentinel Means For Alex In Supergirl Season 6
Although Supergirl is temporarily out of commission and will likely resume her superhero duties at some point in the near future, the series has been building towards Alex becoming a superhero since season 5. In Obsidian’s virtual reality, Alex spent a day as Supergirl following her father Jeremiah’s death. As she navigated her new life sans her role at the DEO, it only made sense for Alex to continue joining her sister out in the field in a more official capacity in Supergirl season 6. While the circumstances surrounding Alex becoming Sentinel are less than ideal, being a superhero sets up her trajectory for the remainder of the season.
Alex has got the suit and an official superhero name. It’s possible she will, along with Martian Manhunter, patrol the streets of National City in a bid to keep people safe. Alex has a bit more control as Sentinel than she did during her time with the DEO because she’s a free agent now. Granted, Sentinel doesn’t have powers like the Girl of Steel, Martian Manhunter, or Dreamer, but she does have the Hand of the Soldier watch and a lot of combat training to make up for it. Alex will likely be shown taking down criminals and answering distress calls in between figuring out how to retrieve Kara from the Phantom Zone.
It’s unclear whether Alex taking over Kara’s superhero responsibilities will be permanent or if Supergirl will abandon her hopes to adopt a baby. Previously, Alex took on the role of DEO director because it allowed her to balance her work and life without needing to be out in the field as often. Thus, allowing her to dedicate more time to motherhood once she was finally approved for adoption. However, now that she’s officially transitioned to being Sentinel and taking on more crucial superhero responsibilities, it’s unclear how Supergirl will handle Alex’s life goals from here on out. Alex’s new role as Sentinel also means she will have to ensure her identity is kept a secret from others. That’s a bit hard considering she doesn’t wear a mask (though neither does Kara), but there’s a chance Supergirl will finally give her one in a future episode. All that said, Alex becoming Sentinel is an intriguing next step in her journey and, as Kara’s sister, she’s a solid choice as Supergirl’s replacement.