Avengers: Age Of Ultron - 32 Easter Eggs, In-Jokes And References
20. Tony Stark Created The Twins
As a call-back to Tony Stark's murky past as an arms dealer, the Twins are shown to be volunteers for Baron Von Strucker's experiments because their parents were killed by a Stark missile.
Their origin also references the Fenris twins in the comics, who were Strucker's own children who he used as part of his nefarious schemes.
Their volunteering is also introduced as an in-joke reference to Captain America's origin. When Maria questions why anyone would volunteer to be experimented on, Cap deadpans:
"Right, what kind of monster would let a German scientist experiment on them to protect their country?"