Viggo Mortensen was always drawn to the old piano in his grandparents’ house in Watertown, N.Y., 30 miles south of the Canadian border, the community where he lived after his parents divorced.

Viggo Mortensen: ‘The criticism of ... “It comes from intimate experience that I’ve had with that disease with my parents, my grandparents, step-father and so on. I mean, some things are ...