Ancient Astronaut Theory - the biggest source

The central premise - aliens visited Earth in ancient times, were worshipped as gods, and built or assisted with monuments like the pyramids - comes directly from Erich von Daniken's Chariots of the Gods? (1968). Director Roland Emmerich said it outright: "When I was in film school, there was a wave of theories about aliens visiting Earth thousands of years ago and being responsible for the pyramids." The franchise basically takes von Daniken's hypothesis and turns it into fiction.

Von Daniken's own work drew from even earlier sources. A 2004 Skeptic article traces the core idea back to H.P. Lovecraft's stories "The Call of Cthulhu" (1926) and At the Mountains of Madness (1931), where ancient alien beings shaped human civilization. The 1960 book The Morning of the Magicians also fed into von Daniken's thinking.

Theoretical Physics - wormholes

The Stargate device itself - a portal creating an Einstein-Rosen bridge - is rooted in real general relativity. Kip Thorne (Nobel Prize-winning physicist) explored wormhole travel in Black Holes and Time Warps (1994) and advised Carl Sagan on wormhole physics for Contact (1985). The concept of traversable wormholes as tunnels through spacetime was theorized by Einstein and Rosen in 1935.

Ancient Egyptian Mythology

The Goa'uld posing as Ra, Osiris, Apophis, and other Egyptian gods is a direct lift from Egyptian religion. The show reinterprets the entire Egyptian pantheon as alien parasites wearing human hosts, a twist on von Daniken's "gods were astronauts" thesis.

Norse Mythology

The Asgard aliens (O'Neill names them after Norse gods) mirror Norse mythology, small gray beings posing as the "gods" of Scandinavian legend, just as the Goa'uld did with Egyptian gods.

Cold War / Military Exploration Narrative

The SG-1 TV series (created by Brad Wright and Jonathan Glassner) took the movie's concept and gave it a Twilight Zone / Outer Limits anthology structure, a military team stepping through a portal to a new planet each week. This drew from military sci-fi traditions and the appeal of episodic exploration.

Carl Sagan's Contact (1985)

Sagan's novel about humanity making first contact through scientific channels, and the cultural and religious shockwave it causes, is a clear spiritual ancestor, particularly the tension between science and faith that runs through the franchise.

TL;DR: The franchise is fundamentally a dramatization of von Daniken's ancient astronaut theory (itself influenced by Lovecraft), grounded in real wormhole physics, layered with Egyptian and Norse mythology, and structured as military exploration sci-fi.