The Swedish tractor manufacturer Bolinder-Munktell (BM) was formed in 1932 with the merger of Bolinder and Munktell, engine and tractor manufacturers respectively. Volvo had begun partnerships in Bolinder-Munktell in the 1940s and purchased BM enitrely in 1950. The Bolinder-Munktell name was retained until the 1970s when the Volvo BM brand came into use. Volvo later sold all its tractor operations to Valmet.
BM Tractors - information from Volvo
BM-sidan.se - site dedicated to BM Volvo