It’s true that Cassius spent most of his life in Kalos and once had ties to gang activity in Lumiose specifically. (He’s very open about both facts, although for obvious reasons, he’s prouder of the former.) However, he also spent some time traveling the world and working for shadier organizations before either of us found him.
Thankfully, this is all in the past, and Cassius has expressed no desire to return to that lifestyle. I’m also rather proud of him because he’s had a clean record for the past few years. He hasn’t even gotten a parking ticket since his time as my protege, that’s how dedicated he is.
Concerning your other question, meanwhile … it may be easier to let Lanette explain.
Bill’s reputation was nothing insidious, really. He just had a tendency to “creep people out,” as the saying goes. You see, Bill spoke up enough in class, but he kept to himself for his first year of college otherwise. That is to say, you only really heard him speak in discussions within a classroom setting—with students, with the professor, that sort of thing. Otherwise, he was known to lurk just about anywhere: computer labs, libraries, popular student spots, class halls—all over campus. He’d rarely speak in those places (largely because he would rarely be seen with anyone to speak to), and he would often be working too hard to make his presence known. So you would be working hard late at night, browsing through the library, and all of a sudden, you’d stumble across a bedraggled little kid with his hair in his eyes like a horror movie cliché, just huddled in a corner at the very edge of your field of vision. Or you’d be walking along late at night from the computer lab across campus, and you’d turn around and find a kid wandering behind you who, up until that point, had been completely silent. People used to call him the “ghost kid” because of things like this.
Those who weren’t unsettled by Bill’s talent of popping up out of nowhere were unsettled by the fact that he was a little kid taking advanced physics. Granted, so was I, but Bill always looked younger than he actually was, especially back then. To make matters worse, he really was rather unapproachable in that he rarely expressed any interest in human interaction and was uncomfortably business-like when spoken to.
In all, before I met him, Bill had been a very difficult case. That is why I wanted to befriend him so badly, actually. He was a challenge. Getting him to be more personable towards humans for the sake of our investors and employers … even more so. —LH
A challenge? I’m not sure whether or not I should be flattered. —Bill
Mm, remember, Bill, I’ve known you for almost a decade. —LH
Ah, true. Well, in that case, I thank you kindly for the compliment. —Bill
The Pokédex According to Bill 