According to articles in the generally reliable Latino Review and HitFix, Ultron will not be the only one making life difficult for the Avengers in the upcoming sequel. If the rumors are true, Baron Von Strucker will be involved as well. In the Marvel Comics, Von Strucker was a Nazi member of Hydra serving the Red Skull in World War Two. He gets hold of a formula that slows his aging so that he survives into the 21st century, mostly unchanged. He rises to become the leader of modern-day Hydra.
If the information in the articles is true, Strucker and Hydra will be the initial villains at the beginning of the film before Ultron comes along. (Think of him like Jabba at the beginning of The Return of the Jedi.) Quicksilver and the Scarlet Witch will be working for him, which will cause the super-siblings to meet the Avengers. Their relationship with the super team is described by director/writer Joss Whedon as “complicated”.
The studio is currently looking for ‘A physically imposing man, age range 40-50, Caucasian, for a supporting role’, which may be Strucker. Two actors who are being looked at for the role are Martin Csokas and Dougray Scott.
The involvement of Strucker could be a bridge to connect Captain America: the Winter Soldier to Avengers: Age of Ultron. The movie will begin filming this spring, and is scheduled for a May 1, 2015 release.