The current study evaluated the interpersonal circumplex as a theoretical model of companion animal personality and companion animal attachment. To this end, the study surveyed 266 companion animal guardians (owners)—89 reporting their most recent pet a cat and 177 reporting their most recent pet a dog—to assess the relationships between interpersonal complementarity and companion animal attachment. The study used MANOVA to evaluate differences in interpersonal traits for cats, dogs, and people who self-identified that cats or dogs were their ideal pets. Results indicated that cats—and people who identified cats as their ideal pet—were more hostile in their orientation than were dogs or people who preferred dogs. In hierarchical regression-analysis, the study also confirmed the positive relationship between interpersonal complementarity and companion-animal attachment.