To the surprise of many, Legends of Tomorrow, a show about a ragtag group of superheroes traveling through time to fix mistakes that they may or may not have made in the first place, has become one of The CW's strongest superhero shows. Less serious than Arrow, with as much girl power as Supergirl, and featuring some of the best characters from The Flash, the show found its stride in season 2 and took off with a bang in season 3. The actors have great chemistry and the storylines are fun.
It was announced that Victor Garber, who plays Martin Stein and one half of Firestorm, would be leaving Legends of Tomorrow midway through season 3 to return to Broadway. (Luckily enough he has shared some of this vocal talent on the show in a couple of episodes including the musical crossover.) Stein has become an integral part of the Legends team, acting as a mentor and the voice of reason as well as some comic relief. He has developed a wonderful fatherly relationship with Jax (Franz Drameh) as the two have spent time honing their Firestorm powers. And as shown after the death of Ronnie Raymond (Robbie Amell), there always needs to be two people controlling Firestorm.
Recently Jax and Martin have been conducting experiments to try to separate themselves with hilarious results and not much luck. So, while Jax has proved he can be a superhero without powers, it is seeming less and less likely that he will be able to operate Firestorm alone. This brings a question to mind: what if Martin doesn't leave to spend more time with his grandson, but something more tragic befalls him? It would be terribly sad to see Martin die after finding such happiness with his family, but it would pave the way for another character to step in to take his place.
From the comics to the Arrowverse, here are 5 other characters who could merge with Jax and replace the professor as Firestorm.
5. Ronnie Raymond
No one really dies in comic books, and that notion has transferred over to superhero TV shows as well. Sure, Ronnie died in season 2 premiere of The Flash by sacrificing himself to save Barry Allen (Grant Gustin), but it doesn't mean we've seen the last of him. The Legends could go and get a different from Ronnie from another Earth (just not Earth 2). Or there could be some kind of Flashpoint explanation for him not being dead or why another version of Ronnie exists. Along with Stein, Ronnie is the original Firestorm from the comics so it would be nice to have him back.
Movie Pilot pointed out that Robbie Amell was in Vancouver recently - and hanging out with White Canary actress Caity Lotz and Danielle Panabaker, who played his onscreen wife Caitlin Snow. While it could be a coincidence, it could also be a clue that Ronnie could return. It would be nice to see both of Stein's protegees working together without him once he is gone.
4. Jason Rusch
In the DC comics, prior to the New 52, Jason Rusch was a high school student who took over as half of Firestorm after the death of Ronnie. (In the newer comics, both Jason and Ronnie can become Firestorm independently.) Jason would be a good replacement for Stein and he has even appeared in the Arrowverse already. In season 1 of The Flash Jason, played by Luc Roderique, was a scientist who worked in Mercury Labs. He previously worked on the FIRESTORM project along with Professor Stein. In the episode he helped Caitlin learn more about the project and then was never seen again.
Since Jason already exists in this universe, it would be easy to reintroduce his character via flashbacks before he joins the team. He could even be recast if necessary, which has happened before with several characters throughout the Arrowverse. Jason has scientific knowledge like Stein and can help the Legends in that capacity as well as bonding Ray (Brandon Routh) over their shared scientific passions. Having Jason on Legends of Tomorrow would be a nice way to pay homage to the original comics while still staying true to what has already been established.