Pity the literary supporting character. Unlike television, which has never met a minor supporting character it doesn’t want to parlay into an uneven, unwatched spinoff, literature by and large leaves many of its most interesting characters languishing in the background, unexplored and mysterious. They’re like the kids who join the Chess Club and win the state championship, only no one notices because some teenage wizard just burned down the school.

Thing is, these secondary characters are even more interesting because of the lack of information about them. The main characters? We know everything. The whole story is about them. The half-glimpsed supporters are like a song that earworms you but can’t be identified. They stick with you, and you wonder…and wonder, with no hope of revelation. Here are five supporting characters we wish had their own books:

Susan Pevensie (The Chronicles of Narnia, by C.S. Lewis)

Susan is one of the most mysterious characters ever created. She’s one of the original band of four children who stumble unto the magical world of Narnia in The Lion, The Witch, and the Wardrobe, of course. But in the final book, The Last Battle, everyone associated with Narnia is summoned back—except Susan. With only vague hints suggesting a reason for her exclusion, the mystery inspired Neil Gaiman to write the short story The Problem with Susan in 2005. While we know why she was booted–too much nylons and lipstick–the world would love to know what Susan did with her family-less life after she was lost to Narnia forever.

Mycroft Holmes (Sherlock Holmes, by Sir Arthur Conan Doyle)

Sherlock’s older brother, Mycroft, has not only demonstrated himself to be even more brilliant, he also has a mysteriously “necessary” job with the British government. We can imagine Mycroft as a spy or secret agent type, as Stephen Moffat has in the modern-day TV series Sherlock, but imagine is all we can do, because Mycroft and his lazy brilliance only appear in four of Doyle’s stories about the world’s most famous detective. Brilliant, socially inept, and a secret agent? This is a character screaming for a book. Since I always imagine myself as a lazy genius (and am generally half right, according to everyone in the known universe), I naturally think Mycroft should get more attention.

Milo Minderbinder (Catch-22, by Joseph Heller)

One might argue that Milo Minderbinder is not a supporting character but a main character in Heller’s brilliant novel, and one could, in fact, argue that he’s actually the main character in Catch-22. He has three chapters devoted to him (where other characters get just one), after all, and his capitalistic ways and memorable scams—for example, buying fresh eggs for a penny each, selling them for four and a half pennies, then buying the very same eggs back for seven cents, and finally selling them to the army’s mess hall for five cents…and somehow making a profit—are often the aspects of the book people remember. If one of those “get rich quick” books had Milo’s name on it, I would buy two.

Louis Gara (The Switch and Rum Punch, by Elmore Leonard)

Made more famous than he otherwise would be owing to film portrayals (by Robert De Niro in Jackie Brown and John Hawkes in Life of Crime), Louis Gara at first glance is a minor character offering some comic relief and handy plot points in the Leonard universe. But if you pause for a moment and examine the character in each novel, separated by 14 real-world years and an indeterminate amount of time in fiction, Louis becomes much more interesting. In The Switch, he’s a criminal, yes, but a fairly cheerful and optimistic one who isn’t down for actually hurting people. By the time of Rum Punch he’s much more hardened, less thoughtful, and prone to violence. Prison time isn’t known for inspiring people, but there’s a potentially interesting character study there.

Boris Pavlikovsky (The Goldfinch, by Donna Tartt)

Boris is by far the most popular character in Tartt’s Pulitzer-winning novel. Simultaneously shameless and whimsical, and speaking in perhaps the most precisely-rendered ESL patois ever managed on the page, Boris disappears for much of the story only to return and be instrumental at the end—and then disappear again. One wonders what hijinks Boris will get up to in the future, and how many people he’ll get accidentally killed along the way—all of whom will use their dying breath to pat him affectionately on the head and forgive him.

Which supporting character would you most love to read a book about?