In the work of Hieronymus Bosch, the threat level is always “Imminent.” While other artists in 1500 were trying to depict the world realistically, Bosch was painting the imaginary, the grotesque and the horrific. In his triptych “The Temptation of St. Anthony,” his subject wanders a desert filled with demons. In “The Garden of Earthly Delights,” strange creatures devour one another across a vast and grim landscape.

As the art world prepares to celebrate the 500th anniversary of Bosch’s death in 1516, a series of coming major...