To whom is Ulysses speaking in "Ulysses"?
The speaker Ulysses (the Roman name for "Odysseus") delivers a reflection on old age and mortality to other elderly veterans who may have fought with him in the Trojan wars. His reflection culminates in a rousing speech intended to convince this same audience of warriors to take hold of life again and to find one last great adventure. Consider the following passage:
Free hearts, free foreheads—you and I are old;Old age hath yet his honour and his toil;Death closes all: but something ere the end,Some work of noble note, may yet be done,Not unbecoming men that strove with Gods.
It may be that the gulfs will wash us down:It may be we shall touch the Happy Isles,And see the great Achilles, whom we knew.Tho' much is taken, much abides; and tho'We are not now that strength which in old daysMoved earth and heaven, that which we are, we are;One equal temper of heroic hearts,Made weak by time and fate, but strong in willTo strive, to seek, to find, and not to yield.
The speaker, the fictional Ulysses, is speaking to an implied audience in Tennyson's poem named after him. The poem is a dramatic monologue, although the silent listener is an implied audience--so there is more than one silent listener.
Ulysses says "You and I are old." The "you," here, is presumably plural. He may be addressing his former followers who returned home with him after his adventures, although this would alter the story as written by Homer in The Odyssey."
Ulysses also addresses his audience as "my friends." Thus, the reader knows he is addressing more than one person. The poetic dramatic monologue form was new at the time Tennyson wrote the poem, so the convention of only addressing one silent listener was not well established.
In short, then, Ulysses is talking a group of followers, old men as he is, into going on an adventure with him.