Education and early career

Born in Brooklyn and growing up as a comics fan, Mantlo attended Manhattan's High School of Art & Design. In college at the Cooper Union School of Art, he focused on painting and photography. Following his graduation, Mantlo held various civil servant positions and worked as a portrait photographer.

Marvel Comics

A connection with a college friend in 1974 led Mantlo to a job as an assistant to Marvel Comics production manager John Verpoorten. Mantlo's first credits were as a colorist, as he worked on several issues that appeared between October 1974 and April 1975. Soon afterword, Mantlo wrote a fill-in script for a Sons of the Tiger story in Deadly Hands of Kung Fu, which led to a permanent writing position on that title. While scripting Deadly Hands, Mantlo and artist George Pérez created White Tiger, comics' first Puerto Rican superhero.

Around this time, Marvel's then editor-in-chief Marv Wolfman instituted a policy to avoid the many missed deadlines plaguing the company. The policy was to have fill-in stories at the ready, should a titles be in danger of missing its deadline. Mantlo quickly became the "fill-in king," creating stories under very tight deadlines, many of which did find their way into print. By the mid- to late-1970s he had written issues of nearly every Marvel title.

Later, he became a regular writer at Marvel, notably for the licensed properties Micronauts and Rom a.k.a. Rom: Spaceknight. On Christmas Day 1977, Mantlo's son Adam opened a new present, a line of the Mego Corporation's Micronauts action figures. Seeing the toys, Bill Mantlo was instantly struck by inspiration to write their adventures. Convincing then editor-in-chief Jim Shooter to get the comics license for these toys, Mantlo was hired to script their series. Mantlo and Michael Golden (the artist on Micronauts) took a few bits of colorful plastic and built an entire (subatomic) universe around them, with its own history, mythology, personalities, and even an alphabet. Ultimately, the Micronauts comic won the 1979 Eagle Award for Favourite New Comic Title.

In the same way, Mantlo turned an uninspired toy called Rom into a cosmic odyssey about chivalry, alienation, and what it means to be human.

Other notable work included the creation of the superhero pair Cloak and Dagger, and well-regarded runs as the regular writer on The Incredible Hulk, Iron Man, The Spectacular Spider-Man, and Alpha Flight.

Public defender

By the mid-1980s, he enrolled in law school. Though he continued writing for Marvel, his workload began to decrease. He wrote briefly for DC Comics in 1988, scripting the Invasion! miniseries. By this time he had passed the bar exam, and was engaged in full-time work as a Legal Aid Society public defender in the Bronx.

Tragedy

On July 17, 1992, Mantlo was struck by a car while rollerblading. (The driver of the car fled the scene and has never been identified.) Not wearing a helmet at the time, Mantlo suffered severe head trauma and spent over two weeks in a coma. He has since been institutionalized, and is not expected to fully recover. Mantlo now resides in the Queens Nassau Rehabilitation & Nursing Center, where he must have 24-hour assistance. His care has long since used up his health insurance. In 2007, cartoonist David Yurkovich released the benefit book Mantlo: A Life in Comics, with all proceeds from the book donated to Mantlo's brother and caregiver, Michael Mantlo, to help toward the costs of maintaining Mantlo's care. In addition, Floating World Comics sponsored Spacenight: A Tribute to Bill Mantlo, an art show made (almost) entirely of various artists' interpretations of ROM, to help raise funds for Mantlo's care.

Mantlo was married to Karen Mantlo (née Pocock), for some years a letterer in the comics industry. They have a son, Adam, and a daughter, Corinna (born in 1981).