In 1912, Deere & Company president William Butterworth (Charles' son-in-law), who had replaced Charles Deere after his death in 1907, began the company's expansion into the tractor business. Deere & Company briefly experimented with its own tractor models, the most successful of which was the Dain All-Wheel-Drive, but in the end decided to continue its foray into the tractor business by purchasing the Waterloo Gasoline Engine Company in 1918, which manufactured the popular Waterloo Boy tractor at its facilities in Waterloo, Iowa. Deere & Company continued to sell tractors under the Waterloo Boy name until 1923 when the John Deere Model D was introduced. The company continues to manufacture a large percentage of its tractors in Waterloo, Iowa, namely the 7R, 8R, and 9R series.