J.A.R.V.I.S.

"Test complete. Preparing to power down and begin diagnostics..." "Uh, yeah, tell you what. Do a weather and ATC check, start listening in on ground control." "Sir, there are still terabytes of calculations required before an actual flight is..." "Jarvis... sometimes you gotta run before you can walk."

- J.A.R.V.I.S. and Tony Stark

Just A Rather Very Intelligent System (J.A.R.V.I.S.) is Iron Man's artificially intelligent computer system. He runs Stark's home and Stark Tower and serves as a user interface in all his Iron Man Armors, giving him valuable information during combat, which is very useful.

Iron Man
J.A.R.V.I.S. was introduced as an A.I. system that controls Tony Stark's house. He also helped Tony develop the Iron Man suit, helping Tony design the suit and run tests and simulations. He later became the user interface for the Iron Man suit, talking to Tony through the suit and informing him of things such as the suit's systems status, atmospheric and environmental conditions and details about enemies during combat.

Iron Man 2
J.A.R.V.I.S. continued to assist Tony Stark in his Iron Man identity, giving him advice on the armor's status and on the enemy's weak points during his battle with Whiplash in Monaco. He helped Stark in creating a new element as a substitute for the obsolete palladium for the Arc Reactor, studying Howard Stark's notes and aiding Tony in his experiments. He helped Iron Man and Black Widow to track Ivan Vanko's signal when he was controlling Justin Hammer's drones.

The Avengers
While Tony was on a date with Pepper Potts, J.A.R.V.I.S. informed him that S.H.I.E.L.D. agent Phil Coulson wanted to meet with him. Tony tells J.A.R.V.I.S. to get rid of Coulson, but this failed when Coulson overrode J.A.R.V.I.S.' system. Later, on the S.H.I.E.L.D. Helicarrier, Tony had J.A.R.V.I.S. hack into S.H.I.E.L.D.'s computers, and discovered that S.H.I.E.L.D. planned to use the Tesseract to create weapons. J.A.R.V.I.S. saved Tony when Loki threw him out of Stark Tower by deploying the Mark VII armor. J.A.R.V.I.S. gave Tony help and advice during the Battle of New York. When Tony redirected the nuclear missile launched by the World Security Council into the Chitauri portal, J.A.R.V.I.S. suggested calling Pepper, to which Tony agreed. However, Pepper missed the call due to being distracted by the news of the invasion. J.A.R.V.I.S. shut down shortly after entering the portal.

Iron Man 3
After the Chitauri invasion, J.A.R.V.I.S. continued to help Tony develop the armors that later became the Iron Legion while Tony was working through his anxiety. After Happy Hogan was caught in an explosion at the Chinese Theater, J.A.R.V.I.S. helped Tony digitally recreate the scene in order to find clues about the bombing. After the Mandarin's forces attacked Tony's mansion, Tony became trapped on the seafloor by the wreckage of his home, but J.A.R.V.I.S.took control of the Mark XLII suit that Tony was wearing and managed to pull him from the wreckage, flying them to the last location that they had discussed before the attack occured.

After landing in Tennessee, J.A.R.V.I.S. began to malfunction as a result of the previous events and was unable to help Tony while he laid low and gathered information on A.I.M. When J.A.R.V.I.S. finally came back online he announced that the wreckage and debris had been cleared from Tony's mansion (removing the wreckage that had been blocking the door to the armor vault) prompting Tony to launch the "House Party" protocol, deploying the Iron Legion as they went to confront Aldrich Killian. J.A.R.V.I.S. then acted as Tony's interface to all of the Iron Legion armor at once, following Tony's orders and remotely setting the directive for the armors to attack all of the Extremis soldiers in the area.

After Killian was defeated, Tony gave J.A.R.V.I.S. the order to use the "Clean Slate" protocol, destroying all of his armors.

Trivia

 * In the comics Iron Man has a butler named Edwin Jarvis. This was changed because Jon Favreau didn't want there to be any confusion between Jarvis and Batman's butler, Alfred Pennyworth. In Iron Man 2: Public Identity it was revealed that Edwin Jarvis was Tony's butler when Tony was a child and when he passed away, Tony created an A.I. after him in memory of his late butler.