Cillian is Todd's less-favorite surrogate parent. He and Todd don't get along, and when Todd describes his "face is covered in annoyance and his Noise is buzzy like mad bees and I can already see myself getting angry and I haven't even properly got home yet" (3.1), we can see why—they're kind of similar.
Cillian's bossy attitude irritates Todd: "It's never been so good with Cillian, not never. Ben's always been the kind one, Cillian's always been the other one, but it's got worse as the day approaches when I'll finally be a man and won't have to listen to any more of his crap" (3.15). Cillian's hardened by years of work, and he doesn't have the sensitive streak that Ben does. Because of this, he fails to really connect with Todd.
But lest you think less of him, Cillian still has a good heart. He offered to help raise orphan Todd when his parents died, after all, and he also wanted to be one of the men to fight the corrupt takeover of Prentisstown. Ben tells Todd: "Cillian […] wanted to do whatever he could to stop them. He would have given his life" (36.118). Rough on the outside? Absolutely. But Cillian's actually a real hero at heart.