Spoilers ahead for the "Therefore I Am" episode of The Flash Season 4.
The Flash spent the majority of the latest episode expanding the backstory of Clifford DeVoe, a.k.a. the Thinker. His backstory was surprisingly emotional and definitely sets him apart from past Flash bad guys, but he wasn't the only DC villain to be mentioned in "Therefore I Am." Wally West returned to Central City after retreating to Blue Valley for some self-reflection, and he revealed that he battled a baddie that now officially exists in the Arrow-verse. Yes, Wally referred to Starro the Conqueror.
Wally didn't come right out and drop the name "Starro the Conqueror," but there's no other villain who could really fit his description of "a starfish from outer space." DC Comics fans will know Starro as a supervillain who first debuted way back in 1960 as the very first villain to face off against the original Justice League of America. It is an intelligent alien with a central eye whose designs on Earth required the united efforts of multiple DC superheroes to be stopped. Capable of spawning asexually, Starro would go on to create a whole lot of duplicates that could attach to the faces of humans and result in their falling completely under his control.
Interestingly, a version of Starro the Conqueror in DC Comics did take control of the Wally West incarnation of the Flash while he was visiting Blue Valley. In The Flash, Wally didn't go into detail of what happened when he faced off against the starfish from outer space, so we can't say if he was or wasn't mind-controlled in the same way he was in the comics. Still, the odds are that he was able to take control of the situation before it got too out of hand. After all, Team Flash knew nothing about an alien starfish until Wally mentioned it. Clearly Starro did not wreak so much havoc as to make the national news and summon some of the other heroes of the Arrow-verse to help.
An invasion by Starro the Conqueror actually could have made for an exciting crossover between the four superhero shows on The CW, although it may not have been possible to bring such a massive and bizarre bad guy to life on the small screen for four hours of crossover action. In the upcoming "Crisis On Earth-X" crossover, the actors playing the heroes will be able to simply double as a lot of the villains. Earth-X is populated by Nazi versions of the characters we've come to know and love, and we'll be seeing some performances from stars who are usually playing good guys.
We'll have to wait and see if Wally's mention of Starro will someday result in Starro making an appearance on The Flash. The show has name-dropped villains before introducing them in the past, as with Gorilla Grodd and Clifford DeVoe. Perhaps Starro will turn up in the future. In the meantime, you can catch Wally and the rest of Team Flash in action in the "Crisis On Earth-X" crossover, which kicks off on November 27 at 8 p.m. ET on The CW. For when your favorite shows will return to the airwaves in 2018, take a look at our midseason TV premiere guide.