William Thomas played Martin in DW: Remembrance of the Daleks, Cleaver in DW: Boom Town and Geraint Cooper in TW: Something Borrowed, TW: The New World, TW: The Categories of Life, TW: The Middle Men, TW: The Gathering and TW: The Blood Line, making him one of the few actors to star in both the classic and new series of Doctor Who.
Indeed, he is the first actor to appear in both the classic and revived series of Doctor Who. Furthermore, he is the only actor to appear in both of those series and Torchwood.