William Thomas
From Tardis Wiki, the free Doctor Who reference
William Thomas played characters in two Doctor Who television stories: Martin in Remembrance of the Daleks and Cleaver in Boom Town, making him one of the few actors to star in both the classic and new series of Doctor Who.
He played Geraint Cooper in the Torchwood television stories Something Borrowed, The New World, The Categories of Life, The Middle Men, The Gathering and The Blood Line.
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.
