Karen is a natural-language user interface created by Tony Stark and installed in the Spider-Man Suit, designed to work alongside and aid Spider-Man in his crime-fighting duties provided that the young hero completed the Training Wheels Protocol.
After Peter Parker discovered that his Spider-Man Suit was being restricted by the Training Wheels Protocol, he had his friend Ned Leeds disable it. Deciding to prove his worth to Tony Stark by locating the source of an illegal arms deal, the Karen A.I. was activated, much to his surprise. There, Karen congratulated him for completing his training and alerted him that he had many different web shooter combinations available. Still working out the improved suit, Parker was exposed to several different web styles in the heat of combat. Shortly after trying to intervene in Vulture's theft, Parker was ambushed by the Vulture himself. After a brief fight atop the moving vehicle, Vulture overpowered Parker and left him unconsciousness in the truck.
Trapped in the D.O.D.C. Vault
- "Karen, you have to help me override that time lock. Lower the voltage and run it."
"Okay, we're just gonna have to try every sequence."
- ―Spider-Man and Karen
Parker later awoke in the Damage Control Deep Storage Vault in Washington, D.C.. Karen informed Parker that the only way out was through the sealed bay doors, which would not open until morning. With seemingly nothing to do but wait out the night, Parker discussed his suit's capabilities with his A.I, naming her "Karen". 
During the night Parker was trapped in the Damage Control safehouse, it came to Karen's attention that a Chitauri power core Parker happened to be holding was a dangerous explosive that detonates when exposed to enough radiation. Remembering that Ned Leeds had another lethal power core with him, Peter Parker immediately looked for ways out. Karen informed Peter that the bay doors could be opened if its security was overridden, but it would take most of the night to try every possible route. Roughly 200 trials into hacking the doors open, morning had come and Parker managed to open the doors. He requested Karen find the fastest possible route to Washington DC, where Leeds was.
- "Karen, uh, give me an X-Ray of the boat and target all the strongest points!"
"Good job, Peter. You have been 98% successful."
- ―Spider-Man and Karen
To be added
Behind the scenes
- Karen was jokingly referred to by director Jon Watts as "J.A.R.V.I.S.' wife", given she is voiced by Jennifer Connelly, the real life wife of Paul Bettany.