Long before costumed superheroes conquered Hollywood, they overran the comic book industry. So of course Superman, Captain America and Wonder Woman are represented in “Geppi Gems,” the Library of Congress exhibition of items donated by comic-book distributor Stephen A. Geppi. But the show’s most intriguing entries are more novel, and often more eccentric, than well-preserved issues of Marvel and DC comics.

Geppi is a native of Baltimore who started his career as a postal worker who sold collectibles at weekend comics shows before opening a small chain of comic book stores. Since 1982, he’s run Diamond, the company that dominates direct distribution of comics in the United States, Canada and Britain. He’s a co-owner of the Baltimore Orioles who opened Geppi’s Entertainment Museum next to Oriole Park at Camden Yards in 2006. He closed it 12 years later and donated much of its collection to the Library of Congress. According to a video interview with Geppi that’s part of the show, he gave the library more than 3,000 items.

These include things of interest to superhero buffs, of course. The show displays copies of two major movie precursors: the 1965 edition of “The Avengers” in which Captain America became the team’s new leader, and the first issue of “Black Panther,” published in 1977. The latter presaged “Icon” and “Static,” lesser-known Black champions introduced in 1993 by Milestone Comics, founded by four African American writers and artists. Those superheroes’ debut issues are here, too.

There’s also a one-of-a-kind superhero illustration: A. Leslie Thomas’s prop drawing of the “Human Key Duplicator,” a device the Joker deployed against Batman — trussed-up, as usual — in two 1966 episodes of the campy TV show. Colored with gouache, the picture is much more vibrant than the washed-out comic books of the same era.

Before the late-1960s boom in superheroes, there were many other comics genres: westerns, sports, horror, science fiction and funny animals are all represented in this array. (Not romance, though.) There’s even an oversize reproduction of the cover of an “all-sports” issue of Creepy, a black-and-white horror comic founded in 1964 and published intermittently until 2016. The show’s earliest items are newspaper comic strips from the 1930s, including a Popeye magazine the show describes as a “proto-comic.”

Geppi is a Disney enthusiast and one of the many devotees of Carl Barks, the writer and artist known for his portrayal of Donald Duck and his clan, notably Scrooge McDuck. Featured here are several Disney mini-comics, featuring Micky, Donald, Goofy and the Seven Dwarfs. (Their creators are anonymous, as was usual for Disney.) The tiny tales were published in 1947 and offered as mail-in premiums in exchange for a Cheerios box top.

That’s not the only connection between comics and breakfast cereal. A pristine uncut and unfolded Cheerios box from the mid-1950s features TV’s Wyatt Earp on the front and a two-sided cutout of a fancy vintage pistol on the back. One side panel shows kids how to build a target range for the cardboard gun; the other features a message from Betty Crocker. “Violence is as American as cherry pie,” as Black leader H. Rap Brown would remark about a decade later.

Another cereal marketing campaign yielded an uncut sheet of Jackson 5 stickers meant as a bonus for Rice Krinkles consumers. They’re grouped here with covers of period magazines featuring Elvis Presley and the Monkees, and a Jimi Hendrix Experience poster. Such material seem a bit off-topic, but rock music was as integral to 20th-century American pop culture as cereal — or gasoline.

And so it is that oddest Geppi gem is a map of the United States produced by the alliance of Walt Disney and the Standard Oil Company of California. Designed to publicize those companies and the 1939 Golden Gate International Exposition in San Francisco, the map is surrounded by panels from “Travel Tykes Weekly,” in which Mickey and Donald make stops on a transcontinental journey. This venerable promo piece seems cynical and innocent at the same time. It’s an amusing curiosity as well as a commentary on a nation that idealizes both the open road and an angry duck with a speech impediment.

Geppi Gems

Library of Congress, Jefferson Building, Graphic Arts Gallery, 10 First St. SE. loc.gov.

Dates: Through mid-March.

Admission: Free. Advance, timed-entry tickets required.