Michael Schneider Variety Editor at Large “Succession” alums Francesca Gardiner and Mark Mylod are here for “Harry Potter.” Gardiner has been tapped to serve as showrunner and executive producer of HBO’s upcoming new untitled series based on the “Harry Potter” books, while Mylod is on board to direct multiple episodes, as well as executive produce. The news was announced Wednesday by HBO and Warner Bros. TV, which are behind the HBO Original series.