When he killed nagini

Probably when he says he'll fight the golden trio in 1st year, or when he stands up to draco and says he is worth 12 of him. Or the obvious killing nagini. Either one.

Everything He Did In Deathly Hollows Part 1 & 2

When he stepped up against voldy and defended Harry at the Battle of Hogwarts.

When he killed Nagni , Happy Bithday Neville

Destroying Nagini with the Sword of Godric Gryffindor!

I think that the battle of Hogwarts was his most heroic moment

Leading Dumbledore’s army

When he told the death eaters in the hogwarts express "hey loser! He isn't here"