Dick is "a nice old guy, forty or so" (6.42) who works as a cook at Philbin's. His main significance to Karl is that he's Karl's Alcoholics Anonymous sponsor, and the two chat at Philbin's a lot about how his life is going. So, even though a lot of the adults in this book tend to screw up a lot, he's one who's actually kind of cool.
While we've already established that there's no way Karl is going to rat out his mom for being irresponsible (we're being kind), Dick seems to know something's up. "From the first days I'd started coming [to Philbin's] for meals, long before I'd started going to AA, Dick had been slipping me extra food," Karl explains. There's also a rumor flying around that Dick is gay because "he dressed neat and fussy" (6.52), but as far as Karl is concerned, the jury's still out on that and he really doesn't care.