Radar is Quentin’s other best friend. Even though Radar is one of the most important people in Quentin’s high school universe, the reader never learns Radar’s last name. Radar’s real name is Marcus, and he was nicknamed “Radar” for a TV character he no longer resembles at all, but the name has stuck. Unlike Ben, who fights back against Quentin and holds his own clear opinions throughout the novel, Radar is much more of a two-dimensional character. Radar is a logical voice of reason throughout the adventures, but he rarely seems plagued with any sort of existential angst.
Radar spends an inordinate amount of time editing Omnictionary, the novel’s version of Wikipedia. He’s constantly trying to improve Omnictionary, building various plug-ins, bots, and hacks to make the system better.
Radar’s parents own the world’s largest collection of black Santas. As John Green has written on his website, these Santas help serve an important symbolic purpose in the novel. Much of the novel is about how we imagine people, and how our image of people in our heads is the same as or different than how those people act in real life. Through the black Santas, Radar’s parents are trying to get us to imagine Santa differently from the dominant narrative.
Radar goes on the road trip to find Margo because he is hard-wired to geek out over logistics and strategies. Essentially, helping Quentin find out about Margo’s location provides Radar another avenue to flex his penchant for figuring things out. But Radar doesn’t appear to change much throughout the novel. He remains a steady, cool, vaguely Spock-like analytical figure. Unlike Ben, who is impulsive but often has good instincts, Radar makes decisions based on calculations rather than intuitions.