At the end of the movie The Amazing Spider-Man 2, a guy meets Harry Osborn in the penitentiary and talks to Harry about unleashing villains like Rhino.
Who's this guy helping Harry? Is he Harry's father?
That man is Gustav Fiers, also known as the "Man in the Shadows". You may remember him from the first film:
Here he visited Curt Connors to ask whether he had told Peter the truth about his father. When Curt tells him to leave Peter alone, he disappears.
In that film, he is credited as the Man in the Shadows. In Amazing Spiderman 2 he is finally given a name, being credited as "Gustav Fiers (The Gentleman)".
A quick search for Gustav Fiers reveals:
It appears likely therefore that he will be some sort of "super villain" in the remaining movie(s).