Growing up with just his brother and the Elder Kettle - Mugman grew up in a family that couldn't make a whole lot of money - what with Elder Kettle being too old to work, and Mugman and Cuphead being too young to settle down with a job. It's not like Mugman didn't /want/ to have a job- as he did find a few part-time jobs every now and again, but he'd prefer to just have fun and spend time with his brother, messing around and getting into as much chaos as he possibly can. Mugman would spend most of his time spending the amount of money he DID make in an arcade he would spend most of his time in, waiting for his brother to come pick him up so they could hangout together.

One day, when Mugman was spending his time in an arcade waiting for the time to passby, he overheard the sound of alarms just across the street. Growing curious, he went to check it out - discovering that just across the street was a bank robbery. Without drawing any attention to himself, Mugman snuck out of the arcade and stealthily pulled his gun out - shooting the robbers in the ankles without looking, all while making sure that he didn't accidentally injure anyone innocent in the process. He was quick to walk away, not wanting to draw any attention to himself- but of course, the only person to notice what he had done was none other than a scout for Hopes Peak Academy. Interested in his ability to shoot and take down robbers from harming anyone without even looking, Mugman received an invitation to join Hopes Peak. Knowing of the success that would follow him should he graduate, Mugman accepts the invitation almost immediately. He's surprised to see that Cuphead is accepted into Hopes Peak shortly after he is, but he doesn't complain about it.

Though, shortly after enrolling in Hopes Peak, Mugman's demeanor started to change just a little bit. He was still a troublemaker and loved causing as much mischief as possible, but he seems to be more on edge and always appears to be on the lookout for /something/. Wonder why.