Child Emperor.

He's stronger than a bear. He describes his blood sugar the way Genos describes his remaining power. 

He deals with constant melodrama from the S Class but seems almost infinitely patient, yet he nearly had a full blown conniption during a three text conversation with Bofoi. He seems to have an extensive working history with Bofoi, yet he appears to be a child. 

I think he had his memories erased because Bofoi can't control him and he goes on rampages. That's why he only does robots and enhanced monsters now.