After Avengers: Age of Ultron trailer #3 release, everyone is talking about Vision's short appearance in the trailer. Who is he? Why is there buzz for him? Scarlet Witch is also there from comics, and didn't create such buzz.
Who is Vision? He is a synthetic human played by Paul Bettany. From the EW - 'Avengers: Age of Ultron': Why Quicksilver, Scarlet Witch and The Vision will fight the bad fight:
The Vision, a synthetic, superpowered human designed by Ultron to show he has the power to create life, too.
Vision will be portrayed by Paul Bettany, who has already been a part of the Marvel movie universe as J.A.R.V.I.S., the Siri-like artificial intelligence who serves as Tony Stark’s laboratory sidekick.
Marvel didn’t release any images of Bettany in costume as The Vision, but EW saw test footage of his make-up while on the set of the movie last month. While his face seemed to be a little more on the purple side of the spectrum than orange, the overall look of the synthezoid has a slightly more technological edge than the original 1968 introduction. He’s a bit more Borg and a little less Crayola.
But for the first time, Bettany will be turning up on screen in a Marvel film—instead of just supplying a voice. “By his own admission, he’s very disappointed that he actually has to show up this time,” Downey says.
The description "designed by Ultron to show he has the power to create life" isn't quite how I would describe it. "Designed by Ultron to give himself a living body" is closer to the truth.
Interestingly, in the promo art there is this image, which gives a different origin to that of Vision.
Programmed by the combined geniuses of Tony Stark & Bruce Banner and imparted with the ability to fly, project intense energy beams[,] and change the density of his form, the Vision has proved himself a worthy hero, aiding the Avengers in their struggle against the evil A.I. Ultron.
While Vision is imprinted with some of Jarvis' programming, I wouldn't go so far as to say he was programmed by Tony Stark or Bruce Banner.