Marc Blackburn is a character in the Global Defense Department story 'Out of Town Visitors'. He is a high-level assassin in the Basileus crime syndicate.His code name is 'Karibdis'. He mainly works with his wife and fellow assassin Michelle Sandoval, code name 'Specter'.
At the time of 'Out of Town Visitors' Blackburn is thirty-three and lives in the city of Iopolis on Canceron. Both he and Sandoval are enlisted by Carl Tolan to travel to Caprica and eliminate Saranna Preece, Maurice Gordon, Jack Bowman, Claire Ratliff, and Christopher England.