The Caterpillar Tractor Company was formed in 1925 with the merger of the Holt and Best companies. Both had been independantly developing and manufacturing tracked machinery, Holt having acquired the patents of the Hornsby company of England, which had also developed early tracked steam engines. Although heavily involved in the farming market during the early and mid 20th century, Caterpillar began to focus on construction equipment as tractors with rubber tires came to dominate the farming market. In 1987, Caterpillar reentered the agricultural market with the Challenger line of rubber-tracked tractors. In 2002, Caterpillar sold the line to AGCO who manufacture the tractors under the AGCO Challenger brand and sell through Caterpillar dealers.
Caterpillar Inc. - offical site
AGCO Challenger - official site
AMCOC - Antique Caterpillar Machinery Owners Club
Antique Caterpillar Machinery Enthusiasts - antique Cat forums
Caterpillar Skid-steer loaders - information on Caterpillar skid-steer loaders at DiggerData.com