Here's a long but hilarious article called "Desperately Seeking Susan" by a lesbian English professor at Stanford named Terry Castle exposing her former idol, the late Susan Sontag, as a massive egomaniac.
Yet, egomania provides confidence and confidence is essential to charisma, and, clearly, Sontag's fame in the intellectual world didn't depend on her writings -- what did she ever write that was memorable besides "The white race is the cancer of human history?" -- but on her personal charisma.
Indeed, much of what we are taught as the high intellectual history of the human race is based more on the magnetism and impenetrable self-assurance of thinkers than on minor issues like whether they were right or not. Freud is a perfect example, a charlatan who befuddled two generations via his implacable self-esteem. Marx was similar, and Ayn Rand was cut from the same cloth but fortunately never had as deleteriously wide an impact as Marx or Freud.
I'd like to make up an honor role of thinkers who were better at being right than being personally imposing. Adam Smith, a classic nerd whose best known anecdote is his falling in a tanning pit in a fit of abstraction while showing Edmund Burke around a leather factory, and the retiring Charles Darwin come first to mind. Until the publications of big books by Edward O. Wilson and Richard Dawkins publicizing his theories when he was approaching 40, the great William D. Hamilton was known only to a few dozen evolutionary theorists. I've never heard anything at all about the personality of Claude Shannon, the Bell Labs engineer who pretty much invented information theory in 1948.
Other suggestions? Lots of mathematician and physicists fall in this mold, but what about in the more politicized human sciences?