Who is the protagonist character in the C.S. Lewis book 'The Silver Chair'?

Well, there are probably two protagonists in this story... Jill and Eustace, who make the journey together, and who both kind of lead the story at different times.

For more on The Silver Chair: http://en.wikipedia.org/wiki/The_Silver_Chair

Answer

Yes the protagonists are definetly eustace scrubb and Jill pole.