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First: McCoy is the Blackstaff, meaning he has both the license and the magical protection to kill with magic. This made him very unpopular with a lot of the council, nobody really likes the Blackstaff, especially when said Blackstaff is also an ornery and opinionated old cuss who often defied the Council even before he was part of it.

Second: McCoy, it turns out, is Harry Dresden's maternal grandfather, a fact McCoy was already aware of but Harry was not until much later in the series.