Axel Storm was a brilliant scientist who invented a helmet that harnessed stellar energies which he could mentally manipulate (shades of Starman!). Clifford Devoe was a former district attorney turned criminal who came upon a thinking cab created by a brilliant scientist. Each man engaged in lawless pursuits in an attempt to gain vengeance for perceived wrongs perpetrated against them.
Axel seemed to believe that Green Lantern murdered his brother Fred during a bank robbery when in fact it was his own helmet that teleported him instead. The helmet linked the Justice League with civilians through their powers and minds until the JLA turned the tables on Storm. Clifford began to experiment with his thinking cap, after years of using other devices against arch-foe the Flash with little to no success, and inadvertently caused his mental "twin", former criminal Artie Perkins, to once more commit felonies... the same ones on Earth-Two that Thinker committed while visiting Earth-One. He faced defeat at the hands of the Atoms of two worlds.
While Thinker had long history of enmity with his world's fastest man alive before battling the Justice Society repeatedly as a member of their opposite number, the Injustice Society, Brain Storm's career was just beginning. After another defeat versus the Justice League, Brain Storm focused his ire against their most powerful member, Superman. Later he attacked members of his family and friends and continued to face defeat. Thinker went from his costumed identity back to his typical suit and tie appearance, then back again, facing a member of Earth-Two Superman's family, Power Girl and her friend Huntress.
Not only was it the helmets that made these two counterparts, nor their penchant for mustaches. Their tendency to wear purple vests, gloves and boots against a blue jumpsuit showed that they had similar fashion sense. And of course, they were schemers and tacticians of the first order... unless they took a chance at matching wits with teams of justice!