Final answer:
The figure closest to being a wise Greek friend and adviser to Odysseus in Greek mythology is Mentor, although other wise Greeks such as Socrates and the centaur Chiron are also notable for their wisdom and guidance in their respective narratives.
Step-by-step explanation:
The wise Greek who was a friend and adviser to the hero Odysseus is not explicitly named in the texts, but the closest figure that fits this description would be Mentor. In Homer's epic, the Odyssey, Mentor is an old friend of Odysseus and is placed in charge of Odysseus's son, Telemachus, and his household while Odysseus is away fighting in the Trojan War and during his prolonged absence thereafter.
The goddess Athena often takes the form of Mentor to offer guidance to Telemachus. However, if we consider wise Greeks in a broader philosophical context, the character of Socrates might come to mind, especially due to his association with wisdom, as presented in Plato's dialogues, although he did not have any direct mythological connections to Odysseus. In terms of historical figures, Chiron, the wise centaur who raised the hero Achilles, might also fit the bill of a wise Greek associated with Greek mythology's heroic figures.