What is "the other?"

Totality and Infinity is a philosophy treatise written by Emmanuel Levinas in 1961. It takes up the question of the ultimate fate of mankind, as well as questions of ethics, theology, and history. According to Levinas, "the other" is any person (or more broadly, any phenomenon) identified as outside of one's own subjective ego. For Levinas, "the other" is a representation of what we cannot grasp through our own limited ego. "The other" represents infinity, eternity, and God. It also represents theological concepts such as boundless love, charity, and an encounter with the Divine.
"I will say this quite plainly," says Levinas, "what truly human is—and don't be afraid of this word—love." For Levinas, it is only through encounters with "the other" that we are able to express and embody love: "To approach the Other in conversation is a teaching [in love]," he says. Approaching the other allows us "to have the idea of infinity," and to experience "the very epiphany [of religion]." For Levinas, encountering "the other" is the only mechanism we have for reaching outside of our limited ego to experience something greater, namely, the mystery of God.