Doctor Phosphorus (Alexander James Sartorius) is a supervillain who has appeared in various comic book series published by DC Comics. Primarily an enemy of Batman, the villain exists in DC's main shared universe, known as the DC Universe.

Doctor Phosphorus appears in the DC Universe series Creature Commandos, voiced by Alan Tudyk.

Doctor Phosphorus first appeared in Detective Comics #469 (May 1977), and was created by writer Steve Englehart and artist Walt Simonson.

Alexander Sartorius was a member of the Tobacconists' Club who wanted to build a nuclear power plant in Gotham City with help from chairman Rupert Thorne. However, he was forced to build elsewhere following public opposition and was transformed into a metahuman during a meltdown at the plant, gaining transparent, burning skin and the ability to generate harmful radiation. He then battled Batman before falling into a nuclear reactor and being presumed dead.

During the Underworld Unleashed storyline, Phosphorus sells his soul to the demon Neron to gain increased control over his powers.

In James Robinson's series Starman, Phosphorus battles Starman and douses him with radiation that will soon kill him. In response, Starman uses his cosmic rod to bury Phosphorus deep underground, apparently killing him.

Phosphorus returns in Detective Comics #825, where he is being held in Cadmus Research laboratories. Cadmus scientists discover that he is no longer human and has had his organs replaced by energy. He eventually escapes before being defeated by Batman and imprisoned in Arkham Asylum.

During Batman's absence after his presumed death, Phosphorus escapes custody and kidnaps Kirk Langstrom and his wife Francine for information about their research. However, Kirk stops him after transforming into Man-Bat.