The Assassination of Wolfgang von Strucker was one of the opening actions in the Ultron Offensive.
During an assault on a HYDRA facility, Phil Coulson downloaded several files that revealed the location of Wolfgang von Strucker, who was using a Sokovian base to conduct illegal experiments with the Scepter Loki wielded during the Battle of New York.
Coulson later relayed the information to former Deputy Director Maria Hill and recommended that the Avengers be brought in.
Several days later, the Avengers launched a surprise attack on the compound and captured Strucker, who was later taken into custody by NATO. During the attack, Stark successfully recovered the Scepter, but not before Wanda Maximoff used her powers to implant a vision of the Chitauri invading Earth into his mind.
Deeply affected, Stark set out to complete the Ultron Program, a peacekeeping program designed to provide a proficient deterrent to any and all threats. The discovery of an artificial intelligence hidden within the scepter's gem prompted Stark and a reluctant Bruce Banner to configure a suitable A.I. structure for the program.
Upon completion, however, Ultron became unexpectedly self-aware and attacked the Avengers during a gala. Following the brief skirmish, he transferred his consciousness to the HYDRA compound and constructed an advanced body before recruiting Wanda and her twin brother Pietro to his cause.