Bill Mantlo is an American comic book writer, primarily known for his extensive work for Marvel Comics from the mid-1970s through the late 1980s. Born William Timothy Mantlo on November 9, 1951, in Brooklyn, New York, he developed an early interest in comics and pursued art education at the High School of Art and Design and the Cooper Union School of Art in Manhattan. His career in comics began in 1974 when he was hired as a colorist at Marvel, but he quickly transitioned to writing, eventually becoming one of the company's most prolific and inventive writers of the era.

Mantlo is credited with co-creating several enduring characters and series, often from unusual origins. He is particularly known for developing the licensed toy properties Micronauts and Rom: Spaceknight into critically acclaimed and expansive comic book series. The Micronauts series, which he developed with artist Michael Golden, won the Eagle Award for Favorite New Comic Title in 1979. Similarly, his work on Rom transformed a simple toy concept into a complex narrative about chivalry, alienation, and humanity. Among his original creations, Mantlo is best known for co-creating the superhero duo Cloak and Dagger with artist Ed Hannigan in 1982, characters whose origins and stories often explored darker, street-level themes. He also co-created the character Rocket Raccoon, who would later achieve widespread fame as a central figure in the Marvel Cinematic Universe's Guardians of the Galaxy films.

Throughout his career, Mantlo was a regular writer on numerous flagship titles, including The Incredible Hulk, where his five-year run was noted for humanizing the character by restoring Bruce Banner's intelligence. He also had notable stints on Iron Man, The Spectacular Spider-Man, and Alpha Flight. In addition to his writing, Mantlo pursued a career in law, graduating from Brooklyn Law School in 1987 and subsequently working as a public defender for the Legal Aid Society in the Bronx. His writing workload diminished as he focused on his legal career.

In 1992, Mantlo suffered a severe traumatic brain injury after being struck by a hit-and-run driver while rollerblading, an accident that left him with permanent cognitive impairments requiring full-time institutional care. The comics community has organized numerous benefits over the years to support his medical expenses. Despite his injuries, Mantlo has been recognized for his significant contributions to the medium. In 2014, he received the Bill Finger Award for excellence in comic book writing. His work has also been adapted for other media, most notably with the character Rocket Raccoon appearing in the Guardians of the Galaxy films; Marvel Studios arranged a private screening of the first film for Mantlo and his family. While not a creator of anime or manga, Mantlo is credited in productions like the anime series Marvel Future Avengers as the original creator of characters such as Rocket Raccoon and Cloak and Dagger, reflecting the enduring legacy of his work within Marvel's global adaptations.