He got name dropped twice during the season and rumors have been swirling every since, now sources are telling TVLine that the villain for the Flash season 4 will indeed by Clifford DeVoe / The Thinker. It started back in March when executive producer Andrew Kreisberg told fans at Paleyfest, "Next season we're not going to have a speedster [as the Big Bad]." I hoped at that point for Rogue War and we'd get Wentworth Miller and Dominc Purcell back. But in the Abra Kadabra episode, David Dastmalchian name dropped DeVoe as one of Barry Allen's greatest foes. Then in the season finale, Savitar / Future Barry time-remnant talked about a device they used to take on DeVoe. Making most fans pretty certain that the Thinker was the non-speedster Kreisberg was talking about.
There have been multiple versions of The Thinker, but the DeVoe version was the original and debuted in All-Flash #12 by Gardner Fox and E. E. Hibbard. He was created as a villain for the Jay Garrick version of the Flash and has no superpowers, just an above average intelligence. In later variations the Thinker would be an artificial intelligence. Just how the television series plans on using him remains to be seen, but since his normal modus operandi is the planning and plotting while other criminals do the actual act, it is possible that we'll get to see more Rogue's next season.
There has been no official confirmation from the CW or Warner Bros TV, but we can already start thinking of casting. Since they're looking to cast a know-it-all named Cliff, perhaps they should go with John Ratzenberger. If they want to continue the "lineage" casting, perhaps they should go with Richard Belzer or Michael Rosenbaum. Or they could go back to the Prison Break well and get Rockmond Dunbar. Or they could go outside the box and get someone who would bring a whole new fan base to the show and cast Christopher Eccleston… at least, that's who I'd like to see.