Definition of "megalomaniac"

'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.'

1929, Sir Arthur Conan Doyle, When the World Screamed‎

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

2013, Jon Huer, Call from the Cave: Our Cruel Nature and Quest for Power, Rowman & Littlefield, page 241