Urban avant-gardist or small-town loony? The Belgian painter James Ensor, who has a survey of hilarious, gruesome beauty at the Museum of Modern Art, is a puzzle to fans and strangers alike, a classic insider-outsider.

He knew all the right art-world people but hated most of them and was sure they hated him. He was an aggrieved traditionalist with a pop-culture itch, equally entertained by Rubens and tabloid cartoons. He was a sophisticated artist who helped shape early Modernism, not in a Paris studio but in an attic room over a novelty shop in a resort town on the North Sea.

Although Ensor has long been a fixture in the art canon, he is also a fugitive presence. My guess is that a lot of people know his name without knowing quite who he is. Who can blame them? He’s hard to pin down. Gothic fantasist, political satirist, religious visionary: one minute he’s doing biblical scenes, the next the equivalent of biker tattoos, in a style that veers between crude and dainty.

Just consider his self-portraits. Within the span of five years in the late 1880s he depicted himself as a cross-dressed dandy, a rotting corpse, a bug, a fish, Albrecht Durer and a crucified Jesus. Clearly that attic room was a crowded, cacophonous place, and the MoMA show, though airily installed, puts us right inside it.