There are several different voices in this poem that put some distance between us and Ozymandias. First there is the speaker of the poem, you know the guy who meets the traveler from an "antique land." It's almost as if the speaker has just stopped for the night at a hotel, or stepped into an unfamiliar bar, and happens to bump into a well-traveled guy. The speaker doesn't hang around very long before handing the microphone over to the traveler, whose voice occupies the remainder of the poem. One can imagine a movie based on this storyline: the speaker meets a strange guy who then narrates his experiences, which make up the rest of the film.
We don't know a whole lot about this traveler; he could be a native of the "antique land" (1), a tourist who has visited it, or even a guy who just stepped out of a time machine. He seems like one of those guys you'd meet in a youth hostel who has all kinds of cool stories but no real place to call home other than the road; he is a "traveler" after all, and he clearly knows how to give a really dramatic description – just note the bleak picture that is painted of the "lone and level sands" stretching "far away" (14) to see what we mean.
Most of the poem consists of the traveler's description of the statue lying in the desert, except for the two lines in the middle where he tells us what the inscription on the statue says; and while the traveler speaks these lines, they really belong to Ozymandias, making him, in a sense, the third speaker in this polyphonic (or many-voiced) poem.