Tiresias is a figure from Greek mythology and literature, the blind soothsayer who appears in Book xi of The Odyssey. Being the most renowned prophet of the non-biblical world and cursed by the gods to live a transgendered existence for seven years until turned back into a man, Tiresias was a useful figure to a wide variety of authors, both ancient and modern, including T.S. Eliot who identifies him (according to the author's own notes) as playing a key role in The Waste Land. The question for readers is this: what feature of Tiresias allowed Eliot to incorporate Tiresias into his landmark poem of the early twentieth century?
The answer seems to lie in his having been both man and woman. In other words, in his own self and in his own myth he served as a kind of bridge between the classical world and modernity - just the sort of thing Eliot was looking for.
The reader observes this in the section of The Waste Land where the clerk and the typist appear. In Section III, "The Fire Sermon", the unnamed typist goes about her life in a mechanical way, in a kind of bondage to the industrial god. The poet intends her to be an archetype of all modern women. In the same way, the clerk who in Section III arrives home to a supper of "food in tins", exemplifies the modern working man. Both the male clerk and the female typist inhabit the lowest place - not in terms of wealth or society, but in terms of their humanity. Later in this section of the poem, Tiresias recounts how "he has walked among the lowest of the dead", thereby establishing his connection with both sexes which have been rendered subhuman by modernity.
Thus, reimagined in the poem, Tiresias serves as a unifying figure in The Waste Land, linking the ancient and modern worlds, rebuilding a myth of unity in the modern world. In The Waste Land, so full of despair and disorder, the reimagined Tiresias reactivates his ancient role - that of prophet. In this mythological context, Eliot appears to indicate that the state of the waste land will not always be perpetual; it will give way to the great unifications of The Four Quartets.