Cortex Vortex

The Cortex Vortex is a machine built by Dr. Neo Cortex that makes animals already subjected to the Evolvo-Ray become mindless slaves to Cortex.

Crash Bandicoot
The Cortex Vortex's first appearance was in Crash Bandicoot. It made any animal obey Cortex and when combined with the Evolvo-Ray, would make mutants for Cortex. However, it was still at the prototype stage, giving the mutants (Ripper Roo, Koala Kong, and Pinstripe Potoroo) distinct personalities. Despite this, Cortex insisted on using it on his newest mutant, Crash Bandicoot who would "lead my Cortex Commandos into world domination". However, the machine failed to work on Crash, who escaped the castle. Cortex tried a different approach: subject Tawna Bandicoot to the machine. However, Crash arrived in time, burned down the Cortex Vortex along with the rest of Cortex's castle, and saved Tawna.

Crash Bandicoot 2: Cortex Strikes Back
Immediately after the events of the first game, Cortex discovered a new power source: Crystals. After spending a year building a new Cortex Vortex (which would be big enough to enslave the planet), his new sidekick, Dr. N. Gin informs him that he has only found the "Master Crystal". 25 more "Slave Crystals" are needed to power the machine. Fearing his life and realizing that Crash has defeated all of his willing participants, Cortex tricks Crash into gathering the crystals for him, stating that it will help the world. When Crash delivers the crystals, Coco reveals Cortex's true intentions. Cortex tries to escape with the crystals to the Cortex Vortex, but Crash defeats him and leaves him stranded in deep space. Dr. Nitrus Brio then tells Crash that if he gathers Gems, he can blow up the Cortex Vortex, situated in space. Crash does so and Brio destroys the Cortex Vortex.

Crash Bandicoot: Warped
The Cortex Vortex had a very minor, but important role in Crash Bandicoot: Warped. The Vortex, plummeting down to Earth, explodes and frees the evil Uka Uka.

Crash Bandicoot: The Wrath Of Cortex
The Cortex Vortex didn't appear in Wrath of Cortex directly, but it was the name of level 25, the game's final "normal" level. It's one of the game's hardest levels. The level has 155 boxes and 2 gems.

Crash of the Titans
The Evolvo-Ray appears again in Crash of the Titans. It turns out it doesn't just work on animals. Uka Uka is living proff of it and gained a tree body in his boss fight.

Crash: Mind Over Mutant
Brio mentioned the Evolvo-Ray saying that Cortex took credit for it.

Trivia

 * although the cortex vortex was presumably used on all mutants,dingodile and ripper roo both turned against cortex at one point