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

Creating Ultron
During the Attack on the HYDRA Research Base, Tony Stark captured the Scepter, but before that, Scarlet Witch showed him an illusion where all of the Avengers, excluding Stark, were dead and Earth was occupied by Chitauri. Stark realized that the world needed better protection than the Avengers could provide. Together with Bruce Banner, Stark explored the stone that was contained in the Scepter and found an artificial intelligence inside it. Stark found it as a key to a peacekeeping program called the Ultron Program. Within three days, Stark and Banner 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 the Avengers, Rhodes, Dr. Helen Cho and Maria Hill stayed in the Tower, Thor offered the Avengers the opportunity to lift Mjølnir. All, except Natasha Romanoff who did not participate, unsuccessfully tried to lift it; Steve Rogers managed to move it slightly. Suddenly, a sharp loud sound happened and Ultron in an Iron Legion body came into hall from laboratory. He described the Avengers as killers and then three drones (now known as Ultron Sentries) broke the wall between lab and hall and attacked the Avengers. One of drones captured the Scepter in the process and flew away. Two remaining drones were destroyed by the team and then Ultron's body was destoyed by Thor. Ultron moved himself into the escaped drone.