Otto Oscar Binder (/ˈbɪndər/; August 26, 1911 – October 13, 1974) was an American author of science fiction and non-fiction books and stories, and comic books. He is best known as the co-creator of Supergirl and for his many scripts for Captain Marvel Adventures and other stories involving the entire superhero Marvel Family. He was prolific in the comic book field and is credited with writing over 4,400 stories across a variety of publishers under his own name, as well as more than 160 stories under the pen-name Eando Binder.

Born in Bessemer, Michigan, Otto Binder was the youngest of six children born into a German-Lutheran family that had emigrated from Austria a year earlier. They settled in Chicago in 1922, during a period rich with science fiction, which enthralled Binder and his brother Earl. The two began writing in partnership and sold their first story, "The First Martian" to Amazing Stories in 1930; it saw publication in 1932 under the pen name "Eando Binder" ("E" and "O" Binder).

Not earning enough as a writer, Binder and his brother worked at many jobs. Earl found employment at an iron works. In late December 1935, Otto Binder began working for Otis Adelbert Kline as a literary agent in charge of Kline's New York City office most prominently marketing the stories of Robert E. Howard, although insufficient business during this Great Depression era forced Kline to close his company after a year and a half. At the time of Otto's move to New York City, Earl Binder dissolved the writing partnership, and all new material produced under the name of Eando Binder from January 1936 on, was solely the work of Otto Binder. Concurrent with his agent work, Binder was writing for Mort Weisinger, editor of Thrilling Wonder Stories, and Ray Palmer, editor of Amazing, for the latter of whom he created the Adam Link series.

Binder entered comics in 1939 on the heels of his artist brother, Jack, who moved to New York to work at the studio of Harry "A" Chesler, one of that era's "packagers" who provided outsourced content for publishers entering the new medium of comic books. The following year, magazine publisher Fawcett Publications began its Fawcett Comics line, and Binder started writing the exploits of such characters as Captain Venture, Golden Arrow, Bulletman, and El Carim. After a year, editor Ed Herron had Binder tackle Fawcett's most prominent character, the superhero Captain Marvel. He soon wrote for the spin-off features starring Captain Marvel, Jr. and Mary Marvel, the latter of whom he co-created with Marc Swayze.

Binder spent from 1941 to 1953 with Fawcett, writing "986 stories ... out of 1,743, over half the entire Marvel Family saga", per comic-book writer-editor E. Nelson Bridwell. His first Captain Marvel writing was the "Dime Action Book" novel Return of the Scorpion, featuring the villain from the 1941 Republic serial The Adventures of Captain Marvel. His first Captain Marvel comic-book story was "Captain Marvel Saves the King" in Captain Marvel Adventures #9 (April 1942). He wrote for numerous other Fawcett features, as well as many two-page text fillers that were required in comics in order to be eligible for magazine postal rates. His text stories in Captain Marvel Adventures, under the "Eando" pseudonym, starred Lieutenant Jon Jarl of the Space Patrol. During his time at Fawcett, Binder co-created with Swayze and C. C. Beck such characters as Mary Marvel, Uncle Dudley, Mr. Tawky Tawny, Black Adam, and Mr. Mind, as well as two of Doctor Sivana's four children: the evil teens Thaddeus Sivana Jr. and daughter Georgia. Binder and Beck unsuccessfully attempted to launch a newspaper comic strip featuring Mr. Tawky Tawny in 1953.

Binder left Fawcett when the company shut down its comic book division in 1953, but found no shortage of work. For Timely Comics, the 1940s company that would evolve into Marvel Comics, he [co-]created Captain Wonder, the Young Allies, Tommy Tyme and the patriotically themed superheroine Miss America, and wrote for stories starring Captain America, the Human Torch, the Sub-Mariner, the Destroyer, the Whizzer, and the All-Winners Squad.

For Quality Comics, Binder co-created Kid Eternity, and wrote Blackhawk, Doll Man, Uncle Sam and Black Condor stories. For MLJ Comics (subsequently known as Archie Comics), he wrote stories starring Steel Sterling, the Shield, the Hangman, and the Black Hood. At Gold Key Comics, Binder co-created Mighty Samson and other characters. His science fiction for EC Comics includes "Lost in Space", illustrated by Al Williamson, in Weird Science-Fantasy #28 (March–April 1955).

In 1948, Binder began working for DC Comics, then known as National Periodical Publications, swiftly creating Merry, Girl of 1,000 Gimmicks, in the feature "Star-Spangled Kid", whose place Merry soon took in Star-Spangled Comics.