The Monster Men is a 1913 science fiction novel by American author Edgar Rice Burroughs, written under the working title "Number Thirteen".

Cornell University professor Arthur Maxon, who has been experimenting in the creation of artificial life, travels with his daughter Virginia to one of the remote Pamarung Islands in the East Indies to pursue his project.

In Singapore, Maxon commissions Dr. Carl von Horn to take them the remainder of the way to their destination in his yacht the Ithaca, and then to assist him in his experiments.

Maxon and von Horn begin their experiments, growing several living creatures in chemical vats, humanoid but mindless and ugly.

Maxon hopes Experiment Number Thirteen will result in a perfect human being, and in his fanatic obsession plans to wed Virginia to this ultimate creation.

Meanwhile, locals including Budadreen, one of von Horn's crewmen, and Muda Saffir, leader of the pirates, conspire against the scientists, who they believe are hiding treasure.

Experiment Number Thirteen indeed appears to result in a physically perfect man, but as soon as the scientists discover this an emergency distracts them.

Maxon, von Horn and Sing Lee pursue the monster, only to find it dead at the hands of Number Thirteen, also escaped from the lab in the wake of the scientists’ departure.

Meanwhile, Von Horn, Maxon and Sing Lee sail to Borneo, encounter the Ithaca, and enlist the Dayaks to take them to Muda Saffir.

Von Horn, Muda Saffir and a group of native warriors happen on the battle and spirit off the unconscious Virginia; Sing Lee, following, sees all.

Then Sing Lee declares Jack is not a monster after all, but an amnesiac he had found drifting in a lifeboat and substituted for Maxon's failed experiment.

The pursuit finally ends at the site of the buried "treasure," which von Horn has dug up; his headless body is found next to the opened chest.

Galaxy columnist Floyd C. Gale, discussing the 1963 reprints, said that "although this book suffers from some of Burroughs's worst writing, there is still a lot of excitement in his tale".