Plenty of candidates for the maker:

"The original 400 Whelen was developed by a group of experienced and knowledgable men back in the 1920's. Townsend Whelen, James V. Howe and barrel maker Adolph O. Nieder. I believe that Fred Adolph, who developed the 30 Adolph express, later called the 30 Newton, was also involved in this project. The caliber was a brain child of Whelen, the rifles made by Howe and the barrels were made and installed by Nieder. There is some evidence that Whelen and Adolph corresponded on the 38 Whelen, which died away after Winchester discontinued the 275 grain 38-72 bullet, and likely corresponded on the 400 as well. Of course the rifle makers of Griffin&Howe and Hoffman were involved in making many rifles for Whelen designed cartridges."

http://forums.outdoorsdirectory.com/showthread.php/18621-The-400-Whelen

Clearly, there were two guys who thought they knew what it was.