The Caterpillar Tractor Company was incorporated in 1925, but they were essentially selling rebaged equipment made by companies Holt and Best until 1927 when they created the "Model Twenty." A total of 8,201 were built to this spec through 1931.

If you want to really nerd out about this and other cool CATs (zing) you should check out Caterpillar Chronicle: History of the Greatest Earthmovers By Eric C. Orlemann

Image: Caterpillar