From the experts:
Though to most Americans Viggo is a one-person name attached to intense actor Mortensen, it is actually an old Norse name dating back to the Vikings, and is currently the 32nd most popular appellation in Sweden. Viggo Mortensen is a Jr., sharing his name with his Danish father. We think this name is so, well, vigorous, that it might appeal to others as well. Taylor and Natalie Hanson seemed to agree when they chose it for their fourth child.