The scientists of Aztec King Montezuma IV tempered with Quinn's timer. They opened a mini-gate and were killed by a tunnel that emerged from it. The opening of the mini-gate drastically cut the time remaining until the next window of opportunity. (Sliders comic Blood and Splendor)
Doctor Paul Morrow (Roads Taken Online Slide on Sci-Fi.com)
Quinn's double from the pilot - The one who gave him the final part of the equation. This double was later seen in "The Other Slide of Darkness," where it is revealed that he was also the one responsible for teaching the sliding technology to the Kromaggs. The double later arrived on the Fog Earth, where he became a god to the local Foggins.
Into the Mystic: The Quinn Mallory who lives on this earth is a slider. However, he does not live on his home earth.
Double Cross: Arturo's double of this earth slid, but not willingly. He was pushed into the vortex by Logan St. Clair. He died because the sliding technology was not yet perfected. On this earth, Arturo invented sliding.
World Killer: Quinn's double invented sliding, and then slid everyone on this earth, except himself, to a parallel earth. Quinn's double did not slide himself until the main group of sliders arrived and Quinn was able to fix his double's sliding technology.
The Alternateville Horror: Rembrandt's double invented sliding which was used so that he, Quinn's double, and Maggie's double, could slide. The three got stuck in the astral plane on the earth featured in the episode. Then Quinn, along with a scientist named John Smith, helped these three slide off this earth.
Ultimatum comic series: Quinn's double invented sliding on the Christian Earth and, following Brother Jacob Milton, used the technology as the harbinger of the God's rapture, transporting the people of this Earth, who arrived to the Satanist Earth. However, due to the crudeness of Quinn's double's technology, they arrived there as pure energy, which could be harnessed by the Satanists. Later, after the original Quinn modified his double's machine, Arturo's double slid together with the original four from the Christian Earth to the Satanist Earth and sacrificed his life to stop the entire ordeal.
Blood and Splendor comic book. A double of Arturo was seen by the Sliders inside the slide tunnel. This double was dressed in biker's clothes and was fighting a giant worm creature, which the Prime Arturo dubbed the "white blood cell" of the tunnel.
The unfinished comic book Get a Life was to have another group of Sliders whose story was very similar to the actual Sliders. Those Sliders returned to their Earth after five years of adventures, just in time to rescue the real Sliders from the mysterious Men in Black.
The Zercurvians perfected their sliding technology by stealing it from various Quinns from various dimensions. (Armada)