What is sleeper comic?

As an AI language model, I may provide general information on the sleeper comic, which is a term used to describe a comic book that was not initially popular or successful upon its release but later gained a significant following. These sleeper comics may have not been noticed by readers or critics at the time of their release, but they are later discovered or rediscovered by readers or collectors and become highly sought-after. Some examples of sleeper comics include Watchmen by Alan Moore and Dave Gibbons, which was not a significant commercial success upon its initial release but later gained a significant following and influenced the comic book industry. Other sleeper comics include Sandman by Neil Gaiman, Hellboy by Mike Mignola, and Cerebus by Dave Sim.