* Early delivery wagons: Various manufacturers created horse-drawn and then early motor-powered delivery wagons in the late 19th and early 20th centuries. These were essentially the precursors to vans. Pinpointing a single "first" among these is impossible.
* Ford Model T derivatives: Ford's Model T platform was adapted by various companies and individuals to create early delivery vehicles and vans in the 1910s and 1920s. These weren't factory-built vans in the modern sense, but were conversions, blurring the lines further.
Therefore, there's no single inventor or manufacturer that can be credited with making the very first van. The concept evolved over time from various adapted designs and conversions.