Cuphead - Lores of Bosses (well, most of em') from SonicDestroyer12

Mhhh… how about, Dr. Khal was a scientist whose inventions were mostly failure. His biggest achievement, a small robot, was the only one that could be called a success. The robot was so very loyal to his master that he looked for the devil and asked for Khal to become the great scientist he always wished, in exchange for his soul. Upon hearing this, Khal used his new talent to make sure his robot was the greatest fighting machine in the world. He may have been a mad scientist, but he was thankful. And he was making sure his robot would never have to hold his end of the bargain.

Mild Spoilers for Werner Werman fight

Perhaps after seeing so much of his brethren killed by the cat, Werner wanted to get revenge and declared war. The battling went on and on, with neither side winning. Eventually, the devil made a deal with him to give him the means to finally kill the cat once and for all, with contraptions and the spirits of his fallen family. However, the deal was that the devil would come for his soul after fulfilling his goal, so he built a robotic doppelganger of the cat to try and trick the devil.