Roy Martin aka Roy Morgan is a burglar and former war-time Radio & Electronics Engineer who listens in to radio police calls, allowing him to stay one step ahead of the cops.
However, aided by his amazing crew, The Third Man was made with an extraordinarily atmospheric look to it, using tilted camera angles and the high-contrast climactic chase through Vienna's sewers (which could have been borrowed from a similar scene in Anthony Mann's He Walked by Night , made the previous year).