The Mad Hatter is a costumed criminal known to have crossed paths with Batman. A master hypnotist, he takes the appearance of the character of the same name in Lewis Carroll's "Alice's Adventures in Wonderland." Cutting edge technology and dangerous implements are hidden in his oversized top hats. Hatter was later recruited to the League of Shadows by Talia al Ghul. One of his notable contributions was bringing the Heretic to full consciousness. Mad Hatter was tasked with brainwashing Bruce Wayne in a compound at the Sisters of Perpetual Grace convent outside Gotham City. Over two weeks later, Hatter barely breached the surface of Wayne's memories and experiences. To him, it was a delicate job threading his way through the layers of the mind. With Wayne, he observed the trauma ran so deep it was as if he defined himself by that pain. Hatter thought it was madness. Talia ordered him to dig deeper, push past the trauma, and locate the child Wayne was before he lost his precious parents then break him. Hatter was annoyed she distilled the task to something so simple.
Heretic interceded and suggested capturing Robin and bringing him to the convent. Talia shot the proposal down. Hatter warned Heretic to stay away from that "rabbit hole." Heretic told him to mind his own business. Heretic disobeyed Talia and kidnapped Robin then threatened Hatter's life if he didn't help transfer Robin's memories. Talia found out and killed Heretic before the act could be carried out. When the convent was stormed by Batman (Dick Grayson) and Batwoman, Talia ordered a retreat. Tusk, Hatter, and Calculator packed the technology up and left. A week later, Talia was informed Batwoman had a hard drive recovered at the convent. Colonel Kane, her father, was brainwashed by Hatter and programmed to assassinate Batwoman. He failed and woke up with no memory of what happened. Hatter infiltrated the World Tech Summit as a busboy. While Bruce Wayne gave his keynote address, Hatter tasered a security guard and took his card. He let in Tusk and Calculator and they made their way to command central.
Hatter tossed his cap for one of his tophats on account he wanted to dress properly for taking over the world. Tusk remarked he was an idiot. Hatter called him a "walrus." At central, Hatter tossed his hat and slit the throats of the two stationed technicians with concealed blades. The trio unpacked their technology and patched into the Watchtower Initiative's systems. Calculator activated power boost and started brainwave synchronization. Hatter remarked there were so many minds and so little time. He began his brainwashing program and recited "The League of Shadows compels you to be one with us. There is no you. You have no home. You have no people." Alfred Pennyworth made his way to central and fought the Calculator. In the skirmish, electrical was overloaded and Mad Hatter's head was blown clean off his neck.