Baron Strucker is HYDRA's big boss following the demise of Alexander Pierce in Captain America: The Winter Soldier, and plays a key role in introducing the Maximoff twins to the story. Sadly, that's about as far as his importance to the plot goes as he's bumped off in the first act of Age Of Ultron. He only lasts about as long as it takes for the Avengers to do a big set piece battle and then work out who the actual Big Bad is, at which point Ultron promptly kills him. He's more of a functional plot-enabler and tetherer of storylines between The Winder Soldier and Age Of Ultron than a proper villain, having only arrived during the credits of The Winter Soldier and then being done away with after about 20 minutes of the film. He's a placeholder for the real villain, in essence; someone for the Avengers to aim their punches at in lieu of anyone else. That's a bit of a shame given his fascinating backstory (in short: 19th century Prussian nobleman and fencing champ fights in World War One, joins the Nazis, helps Red Skull, and professionally aggravates Nick Fury) and his intriguing new take on the monocle. Aside from anything else, the opportunity was there to develop the idea of the Death Spore - the deadly virus which Strucker can release from his body at will, and which would automatically be released in the event of his death - but it was passed over.
