The founder of Wizard Magazine has tended a letter of resignation to the directors of the company, which came into effect last Thursday, reports ICv2.
Rumours had been circulating about Shamus's future with the company following the disappearance of his new blog from its website.
The blog had launched following the disappearance of the Wizard World digital magazine from the internet.
Shamus wrote: "I hereby resign my positions as president, chief executive officer and director of Wizard World, Inc. effective immediately.
"The resignation is not the result of any disagreement with the Company on any matter relating to the Company's operations, policies or practices."
Shamus launched the magazine in 1991, but it suffered a slow decline which saw the cancellation of its print edition and the launch of a digital version earlier in the year.
Wizard has also scaled back its place in the convention market, now running only eight annual shows.