The"I" in the narration is generally assumed to be Chaucer's portrayal of himself in the Canterbury Tales, though the reader can't be absolutely postive that the "I" is definitely Chaucer himself and not a made up narrator character. If the "I" is indeed Chaucer, Chaucer portrays himself as a character on the journey who observes the others. Here is the portion of the prologue where Chaucer refers to "himself" or the narrator's character in first person:
Befell that, in that season, on a day
In Southwark, at the Tabard, as I lay(20)
Ready to start upon my pilgrimage
To Canterbury, full of devout courage,
There came at nightfall to that hostelry
Some nine and twenty in a company
Of sundry persons who had chanced to fall(25)
In fellowship, and pilgrims were they all
That toward Canterbury town would ride.
The rooms and stables spacious were and wide,
And well we there were eased, and of the best.
And briefly, when the sun had gone to rest,(30)
So had I spoken with them, every one,
That I was of their fellowship anon,
And made agreement that we’d early rise
To take our way, as to you I’ll devise.
But nonetheless, whilst I have time and space,(35)
Before yet farther in this tale I pace,
It seems to me accordant with reason
To inform you of the state of every one
Of all of these, as it appeared to me,
And who they were, and what was their degree,(40)
And also what array they all were in;
And with a knight thus will I first begin.
The first time an "I" appears in this passage indicates that the narrator, assumed to be Chaucer, is indeed going on the pilgrimage. He then states that he meets 29 others who will also be on the journey, and speaks with them all throughout the journey, in fellowship. Then Chaucer indicates that he decided to write about each person as he or she appeared to him during this first impression before they left on pilgrimage.