Actor Blair Underwood will take a journey to the past when he traces his family roots as part of TV show. The former Petersburg resident is starring on the next episode of the genealogy documentary series “Who Do You Think You Are?” – which airs Friday night on NBC. On his Facebook page, Underwood recently wrote how much he had learned from being on the show. “I discovered some amazing things about myself and family that I’ve never imagined,” he wrote. Last September, the film and TV star – whose last major role was as president of the United States in the NBC sci-fi series “The Event” – traveled to Cameroon to trace his family history and find long-lost relatives. His father, Frank Underwood Sr., accompanied him on his journey.