Hugh Selwyn Mauberley
The speaker of this poem seems omniscient at times, since it travels across different times and places. But overall, the speaker is most likely Hugh Selwyn Mauberley, who is a sort of stand-in for the poet, Ezra Pound. It's kind of easy to make this comparison because certain versions of the poem actually start with "E.P.: An Ode on the Selection of his Tomb," where E.P. stands for Ezra Pound.
Apart from that, though, it's safe to say that this poem is spoken by the same dude, whether you want to call him Mauberley or Pound. The voice and imagery might change here and there, but it remains pretty clear that this is a poem about Ezra Pound saying what's wrong with the modern world, just as J. Alfred Prufrock was a mouthpiece for T.S. Eliot to talk about the same subject.
When the opening of the poem talks about Mauberley being born in a "half savage" country, you can draw a direct connection to Pound and say that the poem is talking about the United States. The fact that Pound connects the speaker to his own background so early in the poem suggests that we can assume that this connection is there for the rest of the poem.
But why wouldn't Pound just go ahead and use his own name, if he's going to go to the trouble of sticking his initials in there? Well, here's the thing: Pound wants his own experience and his own thoughts to serve as a model for what he'd like other people to start thinking. If he'd used his own name, people would be quicker to write off everything in the poem as the opinions of just one dude. By using Mauberley as a third-person symbolic character, Pound makes his message a little more universal.