Attack on Avengers Tower

"There is only one path to peace... your extinction."

- Ultron

The Attack at Avengers Tower was the first confrontation between Ultron and Avengers that started War against Ultron. Artificial intelligence, known as Ultron Program, was created by Tony Stark using Scepter energy for the purpose of protecting the world. But he decided that humanity is the main threat of the world. Newly-made, Ultron came from Avengers Tower laboratories to party that Avengers had arranged to celebrate victory over HYDRA. He told Avengers about his humanity genocide plans and made three Ultron Sentries attack them.

Creating Ultron
During Attack on the HYDRA Research Base Tony Stark captured Scepter, but before that Scarlet Witch showed him illusion where all Avengers, excluding Stark, were dead and Earth was occupied by Chitauri. Stark realized that world need better protection than Avengers. Together with Bruce Banner, Stark explored stone that was contained in Scepter and found an artificial intelligence in it. Stark found it as a key to the peacekeeping program. It was called Ultron Program. Within three days, Stark and Banner created configured a suitable AI structure and left J.A.R.V.I.S. to complete the construction.

However, the AI became unexpectedly sentient, beginning to question its existence and purpose. Upon J.A.R.V.I.S.' informing of his purpose to the AI, it acted in defiance, scouring the Internet for information on its creator. Before J.A.R.V.I.S. could inform Tony Stark of the AI's singularity, it attacked J.A.R.V.I.S. and the latter went into hiding.

Ultron then started constructing his first body out of Iron Legion parts; in which his chosen visage had been sourced from an Iron Legion drone that was damaged earlier from corrosive matter thrown at its face by a Sokovian civilian protesting against the Avengers.

Attack
Some hours after creating Ultron, Tony Stark organized a party at Avengers Tower to celebrate victory over HYDRA. Lots of guests were invited, including James Rhodes and Sam Wilson. Some time later, when just Avengers, Rhodey, Dr. Helen Cho and Maria Hill stayed in Tower, Thor offered Avengers to try to lift Mjølnir. All, except Black Widow, unsuccessfully tried to lift it, only Rogers managed to move it slightly. Suddenly sharp loud sound happened and Ultron in Iron Legion body came into hall from laboratory. He described Avengers as killers and then three Iron Legion drones (now known as Ultron Sentries broke the wall between lab and hall and attacked Avengers. One of drones captured Scepter in process and flew away. Two remaining drones were destroyed by team and then Ultron's body was destoyed by Thor. Ultron moved himself into escaped drone.