Tennyson (Both the Real-Life Tennyson and a Fictional Persona)
The poem's speaker is Tennyson, who is meditating most immediately upon the death of his close friend, Arthur, and how he gradually came to terms with it. "But wait," you ask, "are we talking about the real-life historical Tennyson, or is this a fictional persona he's making up?"
Good question, Shmoopers. As it turns out, it's actually both. Tennyson really did have a friend named Arthur, and this poem is an elegy for him. So the poem's really personal and uses "I" and "thou" (the familiar form of "you" in Victorian English), indicating that the two were very close.
Throughout the poem, he re-creates a sense of emotion that he experienced when he was with Arthur. Most memorable is the striking image that "Thought leapt out to wed with Thought / Ere Thought could wed itself with Speech" (499-500). Tennyson dwells on the time spent with his friend as some of the best times of his life, and acknowledges it as a loss that he can never fill.
But the poet is also using the speaker-Tennyson to present a universal sort of voice that tackles grief in its various stages. This universal point of view moves through a period of intense grief to a rumination of the life that was lost, and then opens up on more abstract concepts, such as religion, science, and how puny humans can ever hope to make sense of the chaotic randomness of nature or the hidden plan of God.