The Walking Dead's Avi Nash and Callan McAuliffe have been promoted to series regulars for season 9. Nash and McAuliffe play Siddiq and Alden, respectively, and appear to key to the show's new narrative going forward.
Season 8's "All Out War" storyline introduced a number of new characters, including Siddiq and Alden, who have become involved in the war with the Saviors. Siddiq is a survivor who Carl encountered outside Alexandria, as well as the show's first major Muslim character. Alden is the leader of the Savior prisoners Maggie kept at the Hilltop. Of the two characters, only Siddiq is in the source material. Alden appears to be an original character, something that AMC wants to explore more of in the upcoming season.
THR reports that both Avi Ash and Callan McAuliffe have been upgraded from recurring characters to series regulars for The Walking Dead season 9, which will mark both actors' first series regular roles.
Nash's Siddiq was an important part of both Rick and Carl's arcs for this season, as it was Siddiq who inadvertently caused Carl's death. Carl's attempt to save Siddiq was what led him to getting bit. Siddiq has since been allowed to stay at Alexandria, and he's currently using his medical skills to contribute to the community. He was the one who saw to Negan's injury after Rick cut his throat in the season 8 finale. As their resident doctor, Siddiq could grow to become a valued member of Rick's group.
Alden, whose name has been mentioned only sparingly on the show, has gone from a Savior to a member of the Hilltop. After he and several others surrendered, they were locked up at the Hilltop. While others were violent and resistant, Alden was able to serve as a voice of reason. After the Saviors were freed by Simon's attack on the base, most of them fled while Alden and a handful of prisoners decided to remain behind.
Alden has proved to Maggie that he isn't like the other Saviors and would rather them all live together peacefully. He tried to convince Rick to spare the other escaped prisoners, but was unsuccessful. When the war was over, Alden elected to remain with the Hilltop. As Alden has been slowly building trust with Maggie, some fans believe that the character is being set up as a new love interest for Maggie, who is definitely coming back for season 9.
As there are no details yet on the plot for The Walking Dead season 9, it's hard to predict how these characters will fit into the scope of the next season. However, we do know that a civil war between Rick and Maggie may be on the horizon. If so, Alden's distaste for violence could cause him to try to talk Maggie out of going against Rick.