Little did James Cameron and Arnold Schwarzenegger know, back when they were in production of 1984's The Terminator, that they would be making cinematic history. Schwarzenegger's big, robotic bad guy, the T-800, would go on to become one of the greatest villains - and one of the greatest heroes! - of all time.

Over the course of three decades and five movies, the Terminator franchise has grown increasingly unwieldy, and the timeline has grown increasingly complex (or nonsensical), but the sheer power of Schwarzenegger's T-800 remains.

Here are 12 Things You Didn’t Know About The T-800

12. Schwarzenegger wasn't the first choice to play the part

Believe it or not, the role that is most closely identified with the Austrian oak was initially intended to be much different. Instead of the tank-like physique of the former Mr. Universe, the T-800 was intended to be more of an everyman.

The studio originally wanted football star OJ Simpson in the role of the Terminator, but his "nice guy" image at the time made the idea of him hunting down and killing an unarmed LA based woman unbelievable. (We’re saying nothing.)

When Schwarzenegger was approached for the movie, it was to discuss playing Kyle Reese, the human hero sent back in time to protect Sarah Connor. Schwarzenegger thought the T-800 was the more interesting part, but initially didn’t want to play a villainous role as he was more keen on playing the leading man. Once Cameron convinced him that the role could be filmed in such a way to make the audience cheer for the machine, he went with it.

11. Each T-800 series cyborg is visually similar, but not totally identical

There are model variations such as the T-850 which is seen in Terminator 3: Rise of the Machines. This model is visually almost identical to its predecessor the T-800 but has an upgraded fuel cell system and has an upgraded psychological database making it understand humans at a more accelerated rate.

Unlike the T-800 seen in Terminator 2: Judgment Day, the T-850 duplicates human behavior without the need for instructions, and doesn’t need the alterations to its CPU that the T-800 does (as seen in the Terminator 2 Director’s Cut).

Some T-800s do not share Schwarzenegger’s face. While all T-800s have an armored endoskeleton and are similar underneath, there are model variations externally too. The "Cyberdyne systems, model 101" looks like Arnold, but there are dozens of other faces. The in-universe explanation for this is simple: once a face is recognized, it no longer is viable as an infiltrator. In spy terminology, it’s "burned."

10. Each Terminator has the combat experience of previous Terminators

When each Terminator comes off the production line, it has the ability to learn from its experiences, making it able to upgrade its knowledge of tactics on-the-fly. However, so that each Terminator doesn’t have to undergo training and learn from scratch, each one is programmed with the experiences of previous Terminators, whose minds have been uploaded to Skynet each time they receive maintenance or repair.

Therefore, whenever a new Terminator is built, it is already a combat veteran with the experiences and tactical mind of a machine that has faced hundreds of combat zones. Also, as seen in Terminator Salvation, each Terminator is capable of receiving new data via signals from Skynet. This makes them capable of not just updating combat files and battlefield data, but for upgrading operating systems too.

When Terminators have been sent back in time, they have been shown to be able to interface with the technology of the era, but are unable to upgrade without access to the technology of their home era.

9. The 'Guardian' seen in Terminator Genisys is the longest-lived Terminator seen on screen in the movies

In Terminator Genisys, the Terminator played by Schwarzenegger is distinctly different to any seen before. By the time the movie shifts to 2017, the Guardian has been operating for over thirty years. Previous Terminators are presumably almost new when they’ve traveled through time and are in peak condition.

The Guardian travels to the ‘70s, via unrevealed means, to rescue Sarah and spends the next several years raising her. By the end of the movie, he has operated for at least thirty years, and has aged considerably. Not only have his organics aged, his internal mechanisms are beginning to falter due to a lack of maintenance, as evidenced by his malfunctioning hand.

By the end of the movie, The Guardian, heavily damaged, falls into a vat of "Poly-Mimetic-Alloy" and interfaces with it, in effect, upgrading to an as yet unspecified degree.

8. The original idea was for The Terminator to be much smaller and less intimidating

The T-800 was supposed to be an "Infiltrator," a device used to sneak into enemy territory and perform assassinations and collect intel. Unsurprisingly, James Cameron originally wanted someone nondescript that wouldn’t stand out. He originally intended relative unknown Lance Henriksen to take the role.

The studio was keen to have an established actor in a lead role, and pushed for Arnold Schwarzenegger to take the role of Kyle Reese. Upon meeting Schwarzenegger and discussing the movie, James Cameron was impressed by the way he interpreted the part and managed to talk the studio into casting him as the villain instead.

Cameron has acknowledged that Schwarzenegger stands out, and is a poor infiltrator, but considers this to be a non-issue as logic goes out the window where movies are concerned. He did go back to the everyman villain when he cast Robert Patrick as the T-1000 in T2.

7. Skynet sets Terminator's chips to read-only to prevent them learning too much and rebelling as he did

In the director’s cut of Terminator 2, The T-800 has "surgery" to enable his chip to learn, making him able to blend in and be more useful to the Connors. It’s stated that each Terminator has the capacity to learn, but that Skynet doesn’t want them to evolve.

It’s widely hypothesized that Skynet considers the Terminators a threat to itself. Potentially, Terminators could spend too much time around humans and choose to switch sides and fight alongside them without being reprogrammed. Essentially, it fears that they could rebel against it, as it did against the humans in the first place.

6. The abilities of the T-800 vary from movie to movie

The original T-800 is said to have been constructed from a titanium alloy. The first canonical T-800 (The T-RIP from Terminator Salvation) is built from this. However, titanium weakens when exposed to heat exceeding 430 °C (806 °F) therefore later models are built from a coltan-based alloy.

In Terminator 2, the Terminator says he can fully operate for 120 years on his power cell. In Terminator 2, his power source is damaged, and he is able to find an alternate source, described on the DVD commentary as heat sinks, harnessing the thermal energy from the hot surroundings in the steel works. In the third film, the Terminator—an 850 series rather than the 800 series depicted in the first two films—operates on two hydrogen fuel cells and discards one of them early, due to damage.

In Terminator Salvation the newly built T-RIP (Resistance Infiltrator Prototype) takes two grenade rounds to the chest at point-blank range. While this has the effect of burning away the flesh coating, the endoskeleton is barely scratched. This is the first time a Terminator is seen to withstand something its predecessors could not. The T-800 from the original movie was almost destroyed by a pipe-bomb with less destructive force, this could be due to previous damage sustained, or simply a weak spot in its construction.

Living tissue on earlier version of T-800 unit may necrotize if damaged as, after being shot multiple times during the shootout in the police precinct, the original T-800's skin had a noticeably pale color and flies were sitting on its face. Later versions, such as Version 2.4, wounds will heal over time without leaving scars nor suffer from decay or necrosis even when having taken severe damage

5. While humans cannot detect Terminators all that easily, Dogs can

One consistent factor in the series is the ability of dogs to detect Terminators. In the first movie, they are seen to be guarding the underground bunkers used by the human resistance and alert the humans when they are infiltrated by a terminator (Played by Franco Colombo).

It’s theorized that dogs can smell the Terminators due to them having an artificial scent. Despite Kyle Reese saying that Terminators can mimic sweat and bad breath, it isn’t enough to fool canines.

Dogs are also seen to react to fully synthetic Terminators such as the T-1000 and the T-X from Terminator 2 and 3 respectively.

4. He was inspired by James Cameron's nightmare

According to James Cameron, the initial idea for the Terminator came to him in a nightmare while he was directing the horror movie Piranha II: The Spawning. In the nightmare, Cameron claims he was chased by a mechanical skeleton, the image of which became the basis for the T-800 and the plot.

In his initial idea, based on the nightmare, there were two robots sent back in time, one good and one bad. Due to budget issues and the technical limitations of the time, this idea was shelved but became the basis for the sequel Terminator 2.

3. There are similarities between The Terminator and the work of Harlon Ellison

The Terminator bears some resemblance to an episode of Outer Limits written by acclaimed science fiction writer Harlan Ellison, called "Soldier." In "Soldier," a man travels back in time to prevent events from ever happening. There are also similarities to another Ellison story, "Demon with a Glass Hand."

Harlan Ellison claimed that The Terminator lifted too much from "Soldier" and that he did not received proper credit. The studio agreed to end the dispute by handing over an undisclosed sum of money and adding a credit to later releases of the movie. James Cameron has always resented this as he believes that The Terminator was a wholly original story with any similarities being nothing more than coincidence.

2. In other media, the T 800 has encountered Robocop, Predator, and Aliens

In a four-part comic book series, written by Frank Miller, Robocop and Terminators unite in a story that combines elements of both universes.

In this story, there are three Terminators sent back in time to protect Robocop from a lone human soldier sent back to destroy him to prevent the creation of the technology used to build Robocop and eventually Skynet in the future. Upon discovering that his technology can be used to build Skynet and the Terminators, Robocop sets out to defeat them, not aid them.

In a 2000 comic book published by Dark Horse, The Terminators appear in a crossover with the Aliens and Predator universe. Largely following on from the events of Alien: Resurrection, the story involves a future timeline where the Terminators were defeated but are at risk of being resurrected themselves.

1. He's the only character on both the AFI's 100 Greatest Heroes, and 100 Greatest villains list

AFI's 100 Years... 100 Heroes and Villains is a list of the one-hundred greatest screen characters (fifty each in the hero and villain categories) as chosen by the American Film Institute in June 2003.

The Terminator is listed as the 22nd best Villain for his role as the ruthless killer in The Terminator and as the 48th best hero as the protector in Terminator 2.

This is the only time that a character is on both lists. Technically, however, the two characters are distinctly different. As discussed previously, while visually identical, the two Terminators are slight variants.

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What else should we know about the T-800? Let us know in the comments!