Wygan is a vampire and the late-night DJ of Radio Freeform. He broadcasts from the Queen Anne Hill broadcast towers. He plays heavily into the storyline of the series and Harper first meets him in Greywalker (p. 259) after vampire Alice Liddell suggests Harper talk with Wygan about Cameron Shadley.
Wygan is a special type of vampire: an asetem-ankh-astet, or asetem for short. He does not look like a "normal" human as most vampires do. Harper first describes him in Greywalker on page 262 when Wygan has her pinned against the wall: "His eyes glowed, and red fire and white sparks danced jagged lightning strikes around us in a world of roiling, tormented shadow and coiling mist. His eyes were snakelike. His skin gleamed pearlescent and finely marked with tiny, overlapping fringes. His ice white hair was a sculpted ridge that camoflaged the true shape of a saurian skull." In general, the asetem have "fine white skins and cobra forms." (Vanished, p. 174.)
In Vanished (page 222), we learn that, not only is Wygan an asetem, he is the Pharaohn-ankh-astet--the leader of the asetem. Wygan has been planning something for hundreds of years (Vanished (page 222) and has been waiting for a Greywalker to come along so he can "make" the Greywalker into precisely what he needs. Unfortunately for him, it seems that he hasn't quite been able to make Greywalkers before Harper into just what he wanted. When he meets Harper in Greywalker, he pins her up against the wall of his broadcasting booth and implants a bit of Grey into her (p. 263) in another attempt at crafting the type of Greywalker he needs.
According to Marsden in Vanished, the Pharaohn (Wygan) and his followers eat, breathe, and live chaos, giving them power beyond the ordinary vampire. Wygan uses the asetem to cause "mayhem, havoc, and destruction" (Vanished, p. 222) so he can feed off it and become stronger.