The Odyssey's first four books belong not to Odysseus at all, but to his son — a young man who has grown up entirely in his father's absence, surrounded by suitors occupying his own house, and who must find his own courage before he can stand beside the father he barely remembers.
Scholars refer to the Odyssey's opening four books as the Telemachy — a self-contained narrative following Telemachus rather than his more famous father. Encouraged by Athena, who disguises herself as an old family friend named Mentor to guide him directly, Telemachus sets out from Ithaca to seek news of his missing father, visiting the elder statesman Nestor at Pylos and King Menelaus and Helen at Sparta.
Where the word comes from: Athena's disguise as the wise, guiding "Mentor" is the direct origin of the modern English word — a genuinely traceable etymology running straight from this specific character back to contemporary usage.
While Telemachus travels, the suitors occupying his household — aware he is gathering support and information against them — plot to ambush and kill him on his return voyage. He evades the trap, aided again by Athena, and returns to Ithaca to be secretly reunited with his father at the hut of the loyal swineherd Eumaeus, where Odysseus finally reveals his true identity to his son.
From this point, Telemachus is no longer simply the household's vulnerable heir — he fights directly alongside Odysseus in the climactic slaughter of the suitors, the clearest possible proof that the boy who set out searching for news of his father has returned a capable man in his own right.
The same dark postscript: Telemachus also assists in the execution of the twelve household maidservants who had slept with the suitors — the same harsh final act addressed honestly on this collection's Penelope page, rather than glossed over as simple triumphant justice.