MAJOR SPOILERS ahead for Crisis on Infinite Earths Parts 4 & 5.

The Arrowverse's annual crossover event, Crisis on Infinite Earths, concluded with the Legends of Tomorrow episode "Part 5," which ended with a highly-unusual Easter egg: the introduction of Gleek. The episode's final shot was a closeup of an empty Star Labs cage (and a fresh banana peel) with the label "subject name: GLEEK." Who is this mysterious Gleek character, and what does his inclusion mean for the Arrowverse going forward?

Crisis on Infinite Earths resolves the Anti-monitor conflict in a manner very similar to its DC Comics counterpart: by combining all of the major players into one unified Earth, deemed "Earth-PRIME." No longer will the Arrowverse shows exist in isolation from each other. The Legends of Tomorrow episode ended with the Arrowverse's main heroes at their new base, happily chatting amongst themselves; however, the moment was interrupted by mysterious monkey-like noises from off screen. After Sara Lance commented on the animal sounds, the episode cut to the closeup shot of an empty cage. As the door swung shut, the "Gleek" label on its door is revealed.

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Even viewers unfamiliar with DC Comics' characters outside of the Arrowverse can infer two things about Gleek from Crisis "Part 5": because Star Labs is involved, the creature is likely powerful, and, based on the sounds (and banana peel), the creature is a monkey. Looking back at DC Comics' publication history, both of these things are true.

New Superfriends Gleek

Gleek was a blue alien monkey created for the animated series The All-New Superfriends Hour, which aired on ABC in the late 1970s. The show was a Hanna-Barbera Productions series based on the Justice League comics; the show introduced The Wonder Twins Zan and Jayna (loosely based on the Donny and Marie Osmond) and their pet Gleek. Gleek's mischievous antics provided the show's comic relief, following the formula of other Hanna-Barbera shows like The Jetsons (Astro) and Scooby-doo. The character as he originally appeared was able to understand human language, displayed human-levels of intelligence, and had a super-strong prehensile tail capable of stretching. He was also obsessed with bananas. Given the fresh peel shown strewed across his cage, the Arrowverse version of Gleek may share this trait with his animated counterpart.

Gleek has appeared in other DC Comics properties as well. The character appeared in the Superfriends comic spin-off. Most notably, the character experienced a bit of a revival in the 2019 Wonder Twins limited series run. In this version, Gleek is much more realistic in appearance, and seems to be modelled after a capuchin monkey species (sometimes referred to as "organ grinder" monkeys).

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Unlike many of the Crisis on Infinite Earths Easter eggs, the Gleek reference is more obscure, yet its open-ended delivery suggests that there will be more Gleek in the future. The set-up has several implications for the Arrowverse heroes going forward. The reference appeared at the end of a Legends of Tomorrow episode; Legends is the more zany of the Arrowverse shows, and is the most logical home for a character like Gleek. The inclusion of Gleek is a reference to Superfriends, which further suggests that the Arrowverse may be setting up a revival of the much-loved Superfriends series.

Another possibility is that the CW plans to use the momentum of their Arrowverse properties to establish a spin-off show version of the Justice League. The Justice League film was a critical and financial disappointment for DC, so it would make sense for the more-successful TV universe to capitalize on the property. Gleek's original series, The All-New Superfriends, was based on the Justice League comics; therefore, Gleek's inclusion could be referencing this original connection. It remains to be seen if Gleek will even appear onscreen, and if viewers can expect a similar revival of his owners, The Wonder Twins.

More: Crisis Moves All Arrowverse Shows Onto One Earth