In the Odyssey, who does Telemachus call father and why?

Referring to Book XVI, Telemachus comes to the hut of Eumaeus, the swineherd, and finds a beggar there. He talks about his long search for his father but because his father had left when he was an infant, he doesn't know who he is looking for. The beggar reveals himself as Odysseus, telling Telemachus who he is. Telemachus doesn't believe him at first, but understands the truth as Odysseus asks about the suitors to his wife and Telemachus' mother, Penelope. They then begin to plan the destruction of the suitors. Athena plays an important role in this whole process, as she advises Telemachus to oust the suitors (which he was unable to do), then advises him to leave to seek his father, protects and brings him home, and then advises Odysseus to disclose his identity to Telemachus.