What is charisma?

[Lonewolf]

I am interested in people that have a strong sense of presence, you know, the kind that can light up a room or immediately command respect. Charisma can be used for good or evil - but where does it come from and can it be cultivated or learned?
One theory I read recently in a book by Napoleon Hill was that charisma is a type of subconscious emmanation closely related to sexual energy. Ghandi for example, took up abstinence and channelled that energy into bringing down the British Empire and freeing India. Hitler is also said to have been medically impotent and this frustration was the root of his influence.