Legends of Tomorrow is the place to be on network TV for a true ensemble superhero series, and the Legends often need all hands on deck to get out of their various timeline messes. The ensemble got a shake-up in the Season 3 finale when Amaya left the Waverider for her home village, Jax revealed that he's happily married with a daughter and therefore not inclined to run away on time travel missions all the time, Damien Darhk is dead, and Rip Hunter was killed. Kid Flash won't be around in Season 4, and Leonard Snart won't be coming back. Luckily, we now know of one character who will help fill in some of the gaps in Legends of Tomorrow. Courtney Ford, a.k.a. Nora Darhk, has been bumped up to regular status for Season 4.
Nora technically made her Arrow-verse debut on Arrow back in Season 4 as a little girl, but she reached full villain status as an adult on Legends of Tomorrow in Season 3 when she and her father teamed up to try and unleash the time demon known as Mallus on the world. While Nora seemed doomed to die in Season 3 when Mallus took over her body, she was saved when Damien took her place. Damien Darhk died (again), leaving Nora to be locked up for her crimes... or so she thought. Ray, who seemed more than a bit smitten with her, decided to honor the fact that Damien died to give his daughter a second chance, so he gave her Damien's time stone to allow her to escape before the Time Bureau agents could take her to prison. Nora is free and has good reason to owe Ray a favor.
Courtney Ford was a recurring actor in the third season of Legends of Tomorrow, appearing in many of the episodes following her debut in the fifth episode. Deadline reports that she'll be a regular for Season 4, although details about her role are apparently scarce. It's possible that losing her father than then being freed by Ray has given her a new outlook on life and she'll turn away from the villainous path; it's also possible that she'll be yet another problem the Legends will have to face in the fourth season. Interestingly, Ford is actually married to Brandon Routh, who plays Ray. If romance blooms between Nora and Ray, the actors probably won't mind!
If Nora is still a villain in Season 4, at least the Legends can count on having a couple of allies around more often. Matt Ryan was added to the ensemble as a regular, meaning a lot more of John Constantine. Jes Macallan is a new regular as Ava as well, so Sara's love life may be rather complicated in the fourth season! Legends of Tomorrow executive producer Marc Guggenheim also hasn't ruled out Rip Hunter somehow returning to the land of the living, so we'll have to wait and see what happens.