Odysseus was a hero when he fought in the Trojan war. He sacrificed and risked his life for others in his city. A hero is a person that risks their own lives for others safety and security,without even thinking about themselves or the consequences. They are selfless people that do not see themselves as heroes, but the people around them do. Someone who is a heroe, has impulsive actions and can be considered a leader by the people.
I agree that Odysseus is a hero, not only during the Trojan war, but his journey back home after that as well. The way he had his crewman stuff their ears with earwax so only he can hear the song of the sirens was defintely a heroic gesture. However, Odysseus views himself as a hero and is not totally selfless in that regard.