megalomaniac

noun

1. One affected with or exhibiting megalomania.

   “'Well, I don't know him well enough yet to say, but I will admit that if he is not a mere bullying megalomaniac, and if what he says is true, then he certainly is in a class by himself.'”

adj

1. Of, exhibiting, or affected with megalomania.

   “Often, for good measure, Hitler is given as an example of a megalomaniac person. So, for our convenience, Hitler personifies the illness called megalomania[…]”