The stories crafted by artist Steve Ditko and writer Stan Lee harken back to the days of the pulps and Weird Tales magazine. While the word "weird" has come to refer to anything unusual in modern times, it properly refers to the supernatural and the otherworldly, with creatures that human minds can barely comprehend.
This weird brand of horror was the stock-in-trade of writer H.P. Lovecraft, who seems to be a source of inspiration for the upcoming Doctor Strange sequel. The subtitle "In The Multiverse of Madness" seems to be a nod to one of Lovecraft's most famous novellas, At The Mountains of Madness, which detailed a disastrous expedition into the uncharted wilds of Antarctica which uncovered evidence of a fallen civilization and alien monsters. While never directly adapted for film, At The Mountains of Madness did inspire aspects of the movies Alien and The Thing. Guillermo del Toro worked on an adaptation of the story for several years, but it ultimately became one of his 17 abandoned movies.
Much of Lovecraft's work, which has now fallen into the public domain in the United States, has been directly referenced in the cosmology of Marvel Comics. Eldritch beings created by Lovecraft, such as Yog-Sothoth and Nyarlathotep, have appeared alongside creatures inspired by his writing and menaced the likes of Thanos. Chief among these is the Old One Shuma-Gorath, who made his first appearance in an issue of Marvel Premierecentered around Doctor Strange and went on to become a playable character in the Marvel Vs. Capcom games.Between the original Cthulhu Mythos and all the stories inspired by it in books by Marvel Comics, there is a wealth of material for the Doctor Strangesequel to draw upon.