This is a good question. The most cunning person in the Iliad is Odysseus. He shows his cunning or intelligence in a few ways. First, in book two when Agamemnon tells the Greeks that they are departing for home, the only one who is able to see through this test is Odysseus. He also shows intelligence in how he dealt with people. When he came across a common solider he talked harshly to them, but when he approached a leader, he reasoned with them.
Second, in the context of the great argument and hatred between Agamemnon and Achilles, the one who is able to smooth things over between them, is Odysseus. Without the many interventions, Achilles may have left the battle.
In book ten, there is a sneak attack into the Trojan camp by Diomedes and Odysseus. They are able to get important information and they kill Dolon and Rhesos.
Finally, the most famous example of cunning is the story of the Trojan horse. The fullest description of this occurs in Vergil's Aeneid and Homer's Odyssey. Through this trick, the Greeks are able to the defeat the Trojans.