Warning: The following contains SPOILERS for Crisis on Infinite Earths.

The second part of the Crisis on Infinite Earths crossover astonished viewers with a cameo by the coolest character in the Arrowverse; Captain Cold. What made this event even more surprising was just how actor Wentworth Miller was snuck into the episode.

The build up to Crisis on Infinite Earths saw many announcements about actors from earlier television series, cartoons and movies based on DC Comics making appearances as part of the Arrowverse crossover. These ranged from Burt Ward recreating his role as Dick Grayson to beloved voice actor Kevin Conroy playing Bruce Wayne in a live-action production for the first time in history. Yet among all these announcements, nothing had been said about Wentworth Miller returning as an alternate version of Leonard Snart.

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Miller's cameo came early on in Batwoman season 1, episode 9, "Crisis on Infinite Earths: Part 2," when Harbinger traveled to Earth-74 in search of an alternate version of the Legends of Tomorrow's time-ship, which the Arrowverse heroes recruited by The Monitor could use as a mobile base of operations. She was greeted by the ship's computer, who introduced himself as "an interactive, artificial consciousness programmed to operate this vessel's critical systems" named Leonard. When Harbinger replied that she knew who he was, Leonard responded dryly that he was "always pleased to meet a fan."

Captain Cold in The Flash

This line was a shout-out to one of Captain Cold's most famous quips from The Flash season 1, episode 22, "Rogue Air," where Captain Cold noted that he was "always pleased to meet a fan" when he was recognized by the metahuman criminals he helped escape from STAR Labs' secret prison. Coupled with the computer using the name Leonard, this gave a clear indication who the voice was meant to be to those who didn't recognize Wentworth Miller's curt delivery style from the many times he previous placed Captain Cold or his Earth-X counterpart, Citizen Cold.

It is never explained in the episode if Leonard was transformed into a sentient computer program or if he is just based on the personality of the Leonard Snart of Earth-74. It is noted, however, that the Legends of Earth-74 retired after one of their members died and Mick "Heatwave" Rory took over the ship since nobody else was using it. While it seems likely at first that Mick might not have wanted to abandon his best friend and partner in crime, it is revealed that this version of Mick and Leonard have a much more antagonistic relationship than they did on Earth-1, with Leonard needling Mick over his failed attempts at publishing his romance novels and the fact that "you're basically living out of your car." Still, it was nice to see Captain Cold and Heatwave together again in some corner of the Arrowverse, however briefly.

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