Foil
Character Role Analysis
R-13
R-13 confounds D-503, since they're both sleeping with O-90. He's also a poet, something that D-503 once considered doing before becoming a scientist. But I-330 has gotten to R- as well, and as the book goes on, he is used to challenge, test and ultimately help D-503 grow into a more fully formed human soul. Naturally, he eventually gets killed for it, but he's not exactly alone on that front anyway.