At the beginning of the nineties, AEG began developing a modern mixed-traffic three-phase locomotive that was to become the successor to the class 120. The production took place in the former LEW Hennigsdorf, which later came to Adtranz and finally Bombardier. The new shape of the locomotive body was characterized by sloping roof edges and front areas and strengthened the structure. This design came from the draft for a three-phase locomotive of the class 255 of the Reichsbahn and influenced the shape of the later locomotives from Adtranz/Bombardier and partly from Siemens. The prototype, which was only built once, was tested in 1994 as class 128 and was still owned by AEG.

As with the successors, the transformer was already suspended under the frame between the bogies. The two traction converters each supplied power to one bogie and thanks to a total of four GTO thyristors, each axle could be controlled individually. The GEALAIF axle drives developed by AEG were based on a diaphragm coupling and were able to guarantee good cushioning even at very high speeds while being lightweight. Although the wheelbase of the bogies was shorter than usual for better running through curves, this drive allowed very smooth running at speeds of up to 330 km/h on the roller test stand.

The locomotive was approved for speeds of 250 km/h. Although the order for the class 101 express locomotive was won by competitor ABB Henschel, the 12X formed the basis for the class 145 locomotives and thus for the entire TRAXX family. Between 1996 and 1997, it was converted to IGBT thyristors at the ABB plant in Zurich, which would theoretically have allowed operation at multiple voltages. The locomotive modified in this way was now part of the locomotive pool of Adtranz and later Bombardier and was used in a large area. After the turn of the millennium, it was used to test new technologies. Over the years it has carried AEG, UNICEF, Adtranz and Bombardier promotional liveries. Finally, since 2014, it can be found in the Weimar Railway Museum.