Boromir: Noble last stand saving friends.

Haldir: Fighting for the cause of others.

Denethor: Trying to protect his family line from demise.

The Witch King: Trying to prove he is all high and mighty.

Theoden: Trying to prove that the Witch King isn't all high and mighty and helping his Gondor friends.

Gollum/Smeagol: Reclaiming the "preciousss".