The easiest way is probably to use a 2D greyscale image as a depth map to extrude a 3D object. 3D programs will give you more control but you can do this in Photoshop (see Create 3D objects from 2D images in Photoshop - Adobe Support).
This for example, took me a few minutes in Photoshop:
Using this as a depth map:
Chae Byung-rok does have a few other examples of what looks like the same technique, If you take a close up look at this poster, you can see it is made up of completely discrete shapes, individually styled:
Which makes me think this was made in a 3D program (i.e. not Photoshop like my previous example), but using a similar concept.
I'll see if I can come up with a better example later on, I havn't got much time now.
Here's an example made in Blender with the same technique:
In Blender before rendering:
Which was made with this: