Ninjas! And more specifically, Mr. Black! For those who weren't around when he was, Black was a blankface like Mr. X and Mr. Y. (He and Mr. Blank were, in fact, their immediate predecessors/former superiors, and you can actually see the four of them working together a little earlier in this flashback strip.)
We return on Friday, with a new comic and a new round of reader Q and A! Got a question you'd like me to answer about the comic, comics in general, or the world beyond? Pop it in an email with "Q and A" in the subject line and I'll do my best!