Why is Achilles from the Iliad a national hero in the eyes of the Greeks?

He's a national hero, because at the time he was pretty much the only one they could turn to... and his cousin ajax the great... since he was practicly immortal and would of been if his godforsaken mother held him under the fire long enough without peleus interupting, he would of been except for the achiiles heel... he was the best hero but was often shunned and held back by his mother the nereid.. he was saught after because he was immortal