Alfred P. Sloan Jr. and Charles F. Kettering may have had a greater influence on how railroads look and operate today than any others in the 20th century, but many people think they were doctors because a hospital is named for them. You will seldom see them mentioned at all in most railroad museums, because they were the primary architects of the scrapping of 60,000 steam locomotives on the US railroads.
There is a book called My Years with General Motors by Sloan that details a lot of the early GM history including GM locomotives. Kettering is given some coverage as well.
The other book to read is Boss Kettering by Stuart W. Leslie, Columbia University Press, 1983. The book goes into the incredible inventions that Kettering pioneered in the first half of the 20th Century.