Bass and Treble are the evil twins of Megaman
and Rush. They were created by Dr. Wily primarily to
battle Megaman & Rush. While trying to create the
perfect war robot to aid in his evil plots, he stumbled
upon a unique power source called "Bassenium". From that
point on, he created a prototype robot that can harness that
power and named it "Bass". He created Treble to give Bass a
companion.

Because of a malfunction with Bass's programming, he became unstable.
He started disobeying orders and then Dr. Wily all together. He began to
make his own decisions and eventually attacked Dr. Wily. Because of that
attack, Dr. Wily created more robots to destroy Bass. When Bass found out
he asked Megaman to help him to take down Dr. Wily once and for all.

Later in time, Bass confronted Dr. Wily for one last time and discovered that
Dr. Wily was already creating a replacement War robot with "long golden hair".
Bass also disappeared at the same time Megaman did.