Recently leaked merchandising artwork from Avengers 4 reveals potential clues to the Marvel Studios sequel, perhaps most intriguingly with text on the packaging that teases Thor and Rocket Raccoon will face "an even greater threat" than Thanos himself. Considering the Mad Titan wiped half of the universe from existence in Avengers: Infinity War, that's a tall order indeed.
Fans have already began to speculate what, or who, that threat could be, with the Fantastic Four villain Annihilus emerging as a popular theory, which is dependent on the unsupported belief the character was secretly part of an earlier rights swap between Marvel Studios and Fox. It's far more likely this cosmic threat is something that's been hinted at the Marvel Cinematic Universe since 2014. And it's one the Guardians of the Galaxy have confronted at least once before.
First seen in archival footage, and in the long-deceased remains of one of their own, the Celestials have been a presence in one form or another since Guardians of the Galaxy. The head of one of the ancient beings serves as the deep-space travel hub Knowhere, inhabited by Taneleer Tivan, the Collector. While explaining the origins of the Infinity Stones to the Guardians, Tivan shows the team footage of the Celestial Eson the Searcher using the Power Stone to lay waste to an entire planet in the blink of an eye.
Although Tivan implies to the Guardians that the Celestials left the known universe for parts unknown millennia ago, the possibility of their return is left open. Shortly thereafter, the Guardians find themselves in the most personal fight of their lives against a Celestial, in another form.
In 2017's Guardians of the Galaxy Vol. 2, Peter Quill learns he's half-Celestial, which explains why he was able to withstand direct contact with the Power Stone in the original film. Star-Lord and the team meet Ego, who introduces himself as a Celestial and Quill's biological father. By the end of the sequel, the Guardians learn of Ego's secret plot to spread his existence throughout the cosmos by planting portions of his essence across inhabited worlds and engulfing their respective denizens. The Living Planet nearly succeeds, but is stopped by the Guardians bombing his core, killing him and nullifying the Celestial DNA within Quill.
While Ego existed in the MCU for millennia as the only known remaining Celestial, there's a possibility more may survive at the fringes of the universe. Given the death of one of their own, and their connection to the Infinity Stones, perhaps the events of Guardians of the Galaxy Vol. 2 and Avengers: Infinity War could lead the omnipotent race making their return in a big way. The Avengers have faced Celestials multiple times in the comics, including, just this summer, the inaugural arc of Jason Aaron and Ed McGuinness' Avengers relaunch.
With a proven disdain for inferior sentient life, and a penchant for destruction, Ego's death at the hands of the Guardians and Thanos' perceived abuse of the Infinity Stones provide the Celestials with two compelling reasons to recover the powerful artifacts for themselves and use them to wipe out all sentient life in the universe.
Perhaps the new costumes Thor and Rocket wear in the upcoming sequel aren't for exploring the Quantum Realm, as originally theorized. Maybe they're instead for venturing into deep space and taking the fight directly to the Celestials. But given the immense power of these cosmic beings, even without the aid of the Infinity Stones, the Avengers would need all the help they could get to take them down.
The untitled sequel to Avengers: Infinity War will release on May 3, 2019. Directed by Joe and Anthony Russo, Marvel’s Avengers 4 stars Robert Downey Jr., Josh Brolin, Mark Ruffalo, Tom Hiddleston, Chris Evans, Chris Hemsworth, Jeremy Renner, Chris Pratt, Elizabeth Olsen, Sebastian Stan, Benedict Cumberbatch, Paul Bettany, Samuel L. Jackson, Cobie Smulders, Benedict Wong, Zoe Saldana, Karen Gillan, Vin Diesel, Dave Bautista, Pom Klementieff, Scarlett Johansson, Tom Holland, and Anthony Mackie.