Correct capitalisation of "Machiavellian"?
Does the adjective Machiavellian always have a capital letter? For example:
The Machiavellian Iago manipulates Othello into believing his wife, Desdemona, had an affair.
Not sure if this is anything to go by but, Microsoft Word corrects the word to have a capital. I am not sure if this is also the case when it is an adjective.
First, apart from very rare exceptions, you should capitalize all words derived from a person’s name (see here and there, on this very site). It doesn't matter whether it's a noun, an adjective, a verb, anything. Just put a damn capital!
Now, for your specific case, two additional points in support of capitalization:
the New Oxford American Dictionary lists all derivatives with a capital: Machiavel, Machiavellian, Machiavellianism.
of the Corpus of Contemporary American English’s most recent 100 recorded uses of Machiavellian, only 3 use the lowercase.
It's not wrong to capitalise Machiavellian, because it is taken from a proper noun. However, it is such a common word that it is probably not necessary to capitalise it any more.