DC's Legends of Tomorrow will bring back some familiar friends for its 100th episode. During an interview with CBR, showrunner Phil Klemmer revealed the milestone episode will feature the return of Captain Cold, among other past characters.

Asked how Season 7 will approach Gideon as a human character as opposed to an A.I., Klemmer explained she will face challenges along the road to finding her humanity, but the lessons she's learned from the Legends over the years will point her in the right direction. In fact, this journey -- and how far she's come since Season 1 -- will be the centerpiece for the 100th episode.

"Well, there's the mechanical difficulty of her just having a massive AI smushed into a human brain, which wasn't meant to really hold that vast reservoir of just data. Beyond that, she gradually developed humanity," he told CBR. "You know, she was pretty cold and calculating Season 1. She changed with our Legends. Our 100th episode is basically a retrospective of showing how Gideon the computer learned from our Legends' lessons, both good and bad. But for human Gideon, this is the first time she's actually experienced life with the team."

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He added that, for him, the most surprising part for filming Season 7 was the willingness of former cast members to return for the milestone episode -- including Wentworth Miller's Captain Cold. "The most surprising thing is just the old Legends from Season 1 who returned for the 100th episode," he shared. "I never thought that Captain Cold would be back on the Waverider again, but to me, that is the most shocking in the best possible sense."

Miller brought Leonard Snart from The Flash to Legends of Tomorrow in 2016. However, his tenure on the Arrowverse series was short-lived. Captain Cold sacrificed his life to save the other Legends in "Destiny," the 15th episode of Season 1, spelling the end for that iteration of the character. However, he returned as an alternate-world version of Captain Cold called Leo Snart for 2017's "Crisis on Earth-X" crossover and reprised the role for a handful of episodes in Legends of Tomorrow Season 3. He has not appeared in the Arrowverse since then, with the exception of a voiceover-only role during "Crisis on Infinite Earths."

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Notably, Klemmer described Miller as one of "the old Legends from Season 1 who returned for the 100th episode," which suggests other former teammates are on the table as well. He didn't confirm any other characters, but other esteemed Legends alumni continue to be involved with the Arrowverse. For instance, Brandon Routh will return as Ray "The Atom" Palmer for The Flash's Season 7 event "Armageddon," which bows in November.

Other previous cast members who could potentially return include Arthur Darvill as Rip Hunter, Franz Drameh as Jefferson Jackson, Victor Garber as Martin Stein, Ciara Renee as Hawkgirl, Falk Hentschel as Hawkman, Dominic Purcell as Mick Rory, Maisie Richardson-Sellers as Vixen/Charlie, Ramona Young as Mona Wu and Courtney Ford as Nora Darhk.

Legends of Tomorrow returns with its Season 7 premiere, "The Bullet Blondes," Oct. 13 on The CW.

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