The Series 600 Terminator was the first Infiltrator developed by Skynet as an attempt to infiltrate the Resistance. However, Skynet used the rubber skin as the covering sheath for the Series 600 Terminator, which made it easy to be spotted by the Resistance.
Later, Skynet develops new series of the Infiltrator based on mimetic polyalloy, allowing the units to impersonating any person molecularly sampled by physical contact. The first Infiltrator series with mimetic polyalloy is the Series 1000 Terminator and its variants, such as T-1001, T-1002, and T-XA. Those series are entirely composed of mimetic polyalloy, so they are capable of altering its form and appearance into any person or object of similar volume.
At a certain point, Skynet created the Series X Terminator, which used mimetic polyalloy as outer sheath over an advanced metal endoskeleton.
Additional research was put forward into increasingly organic Terminators able to more efficiently evade detection and infiltrate human organizations, such as the TS-300 Stealth Terminator created by MIR or the I-950 Infiltrator.
Additional to the ceramic endoskeleton mimicking human weight and structure for scans, the TS-300 Stealth Terminator uses personality transfer software called "Stealth Infiltrator Personality" to create undetectable one-off copies of real human beings. The TS-300 is equipped with the EM sensor masking/stealth unit which enables it to defeat other electronic detection systems as well.
Unlike other Terminators, the I-950 Infiltrator was born rather than created with technological enhancements added over time; the I-950 starts out as a baby with a neural net processor attached to the brain, providing an uplink to Skynet. Because of I-950's almost purely organic nature, it is harder to detect using metal detectors and is undetected by the dog.
- According to the comic The Terminator: The Dark Years, Skynet tried a new type of infiltration network using rat robots. John Connor discovered that Skynet was not only studying rats but all sorts of animals, even humans.
- In Terminator: The Sarah Connor Chronicles episode "Allison from Palmdale", a similar program may be in play with the reveal that Skynet has captives, small apes, bears, and tigers in an Infiltrator interrogation and production facility on an aircraft carrier.
- In the comic Terminator: Revolution, Skynet dispatched Dire Wolf, a powerful wolf-type Terminator, to destroy the T-Infinity.
- In at least one timeline, the T-799 is the first Terminator with living tissue over a metal endoskeleton instead of the T-800.
- Kyle Reese: The 600 series had rubber skin. We spotted them easy, but these are new. They look human - sweat, bad breath, everything. Very hard to spot. I had to wait till he moved on you before I could zero him.
- The Terminator