>>91774172X-9 (his actual name is X-49) is a very old model of Aku-bot with an experimental emotions chip that made him capable of empathy and desirous of self-preservation. His creator cultivated his personality over a period of years, even giving him a pet to care for, then informed Aku. Aku, of course, kidnapped said pet to emotionally blackmail the bot into attempting to kill Jack.
Ultimately, obviously, he failed. He does have a close design resemblance to Scaramouche, though, and it seems likely that the scatting assassin is a refined version of that old style of Aku-bot.
