Pelo comentário do OP acima, este livro é Molusco Imperador Versus Cérebro Sinistro , por A. Lee Martinez, publique 2012. O resumo do livro em goodreads.com dá uma visão geral do enredo:
Emperor Mollusk.
Intergalactic Menace. Destroyer of Worlds. Conqueror of Other Worlds. Mad Genius. Ex-Warlord of Earth.
Not bad for a guy without a spine.
But what's a villain to do after he's done . . . everything. With no new ambitions, he's happy to pitch in and solve the energy crisis or repel alien invaders should the need arise, but if he had his way, he'd prefer to be left alone to explore the boundaries of dangerous science. Just as a hobby, of course.
Retirement isn't easy though. If the boredom doesn't get him, there's always the Venusians. Or the Saturnites. Or the Mercurials. Or . . . well, you get the idea. If that wasn't bad enough, there's also the assassins of a legendary death cult and an up-and-coming megalomaniac (as brilliant as he is bodiless) who have marked Emperor for their own nefarious purposes. But Mollusk isn't about to let the Earth slip out of his own tentacles and into the less capable clutches of another. So it's time to dust off the old death ray and come out of retirement. Except this time, he's not out to rule the world. He's out to save it from the peril of THE SINISTER BRAIN!