The Bull Tractor Company of Minneapolis, MN, produced a light-weight 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 quot;Little Bullquot; and was build for 2 years. 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 tractors were designed by Henry Wallis- J.I. Case's son-in-law. Their original ad shows they were sold by in Fargo, ND by Cooper Bull Tractor Co.
http://tractors.wikia.com/wiki/Bull_Tractor_Company