Wouldn’t this describe “Star Wars” itself? Alec Guinness was a pretty big star for a film that looked a bit shaky on paper and was filled with unknowns. The whole movie depended on people liking and identifying with Mark Hamill and Harrison Ford and both of whom had few prior movie credits (though at least Ford had the hit “American Graffiti”).
Also, this description fits just about every movie Gary Oldman has been in (especially the unrecognizable part).
And of course, the central character of all the Star Wars films is R2-D2, since Star Wars is the chronicles of R2’s adventures. 
In Operation Crossbow Sofia Loren was billed as one of the two leads in the film. Even in the main poster done of the film, she is in George Peppard’s arms (I think that same pic is used on the video cover - he is the real lead), but in the film she is on screen no longer than five minutes (I do not exaggerate).
By the midichloreans themselves, you’re right! R2-D2 must be the real real real real REAL protagonist! :: d&r ::
True, but nowadays they’re recognizable names. Go up to anybody on the street, ask them who Mark Hammil is, and chances are they’ll say, Oh Star Wars! Say Ian McDiarmid’s name, they’ll say Who?
Gary Oldman is God. I absolutely did not recognize him as Commisioner Gordon in Batman Begins. I think he’s a little more famous than what I’m looking for, though.
I just had to find out the name of this turkey. You might enjoy reading the comments at IMDB’s readout of Chasing Dreams.