The Thinker was a Flash villain who actually resided in Gotham City, a failed lawyer who became the brains behind a team of smaller villains and developed a number of devices, such as the Thinking Cap, which allowed him to exert mental force on others. The mantle was later taken by Cliff Carmichael, and its here that it could tie into the show as he was a rival of Ronnie Raymond, aka one half of Firestorm. Hes just got married to Caitlin, but that happy ending probably isnt going to last, meaning theres a good chance to introduce an enemy from his past, which would tie him into the larger story and provide a different sort of villain for the team to face.