This is a good question. There are many significant things that Odysseus is known for. Let me give you a broad answer and then a more specific one.
On a broad level, Odysseus is known as a wily or crafty person. To be sure he is a great warrior, but he is really known for his cunning and way with words.
On a more specific level, we see his cunning in several ways. First, he is able to mediate between Achilles and Agamemnon. Without Odysseus, Achilles would have left long ago and this would have lead to the defeat of the Greeks.
Second, Odysseus is the one who concocted the idea of a the Trojan horse that eventually lead to the downfall of Troy and granted victory to the Greeks. Also when we look at the Odyssey, we see that Odysseus was able to get out of a lot of trouble through his craftiness. For instance, he esacped Polyphemus, Circe, and finally killed the suitors to regain his power back at home.