It was commonly called the Me 109, most often by Allied aircrew and even among the German aces themselves, even though this was not the official German designation. The designation "Messerschmitt Bf 109 '' was issued by the Ministry of Aviation (German: Reichsluftfahrtministerium) and represents the firm that originally built them, the "Bavarian Aircraft Works '', or Bayerische Flugzeugwerke (BFW) in German. The confusion arises because design work began in 1934 at the BFW firm and, as was customary, the model was designated by the prefix Bf. On July 11, 1938 the company was renamed Messerschmitt AG due to Willy Messerschmitt becoming its new owner, and the prefix Me was applied to all new models after that date, whilst existing types retained their Bf prefix.
what does bf stand for in bf 109
Bayerische Flugzeugwerke