Heinous Helmeted Headmasters

Brainstorm and Thinker, Steve Dayton and Hartford Jackson, four scientist that developed cranial hamlets that enhanced their mental resources. The first two men used these devices for evil, the second two for good. But there two other men who likewise harnessed similar technology… Captain Calamity aka Mister Esper and Professor Gaunt aka Mister Zero.

Mister Esper was a con man who had devised a super sonic whisper device that could induce his victims into following his every suggestion. With this technique at his disposal, Esper even temporarily stymied Batman and Robin of Earth-One in their attempts to defeat is ill-gotten ways. Nevertheless, the Dynamic Duo was successful in circumventing this, although Esper returned when he was employed by a Syndicate to finish the Batman. However, Esper manipulated various enemies of the Dark Knight into protecting the hero and his sidekick, and later made another play as Brainwash versus the pair, which ultimately led to defeat. 

Mister Zero was originally university professor Hiram Gaunt, who theorized the concept of a helmet which could augment a person’s brain power. When rejected by his fellow professors, Gaunt developed the device on his own, which gave him modest telepathic abilities. With this new ability, he began his criminal career first seeking out those who scoffed him, then once eliminating them he became a crime boss known as the Answer Man. This drew him into conflict with Sandman and Sandy of Earth-Two, who eventually defeated him.

Years later, Mister Esper returned under the alias of Captain Calamity, He was capable of tapping into the mental abilities of the young heroine known as Lilith through his helmet,  allowing him to unleash disasters from coast to coast across the United States. This caper drew the attention of Robin, Kid Flash and the remaining core membership of the Teen Titans, as well as the newly formed Teen Titans West. Only with their combined forces were they able to defeat Esper/Calamity, a defeat from which he never recovered as he retired from villainy.

Shortly after his first encounters with superheroes, Professor Gaunt returned and specialized on becoming a master assassin as Mister Zero. He developed variouis calculated "murder methods" for his victims, which led to his battles with and defeat at the hands of the super-speedster Johnny Quick. Then in 1945, Professor Gaunt returned one final time, now wearing the helmet  fulltime which granted him further powers against his foes during a second clash with Sandman and Sandy*.

Interestingly, this same cerebral device utilized by these Gotham villains was also developed and employed by Owlman, the counterpart of the Batmen of Earth-Three. He also used it for evil in his own Gotham City, before first Earth-One's Batman and later Earth-Two's Huntress defeated

* As seen in America versus the Justice Society, when Sandman explained during a congressional hearing the reason for his retirement due to a heart attack, with an image of he and Gaunt in battle. Perhaps the Professor’s helmet induced the heart attack upon his masked foe.