The Bull Tractor Company of Minneapolis, Minnesota, USA, produced light weight prototype 3 wheeled tractor in 1913. They were a twin cylinder 12 hp engined model giving about 5 hp at the drawbar. This first model was Known as the "Little Bull" and was build for 2 years. In 1915 they introduced a larger model with a 25 hp Twin cylinder engine developing 10 hp at the draw bar, this was called the "Big Bull". They had one large and one Small rear wheel to ride level when ploughing. They became one of the biggest suppliers at the time and signed to supply Massey-Harris in Canada, but supply problems meant they could not deliver and the deal broke down. The Bull Co. subcontracted manufacture to another firm who then decided to supply other firms instead.
Following Fords entry into tractor making in 1917, with their simple mass production and cheap price, which lead to a fall in orders for a lot of small manufacturers as Ford signed large orders with the Governments. Subsequently Bull folded within 3 years.