Vexen, the fourth member of the Organization, is my second favourite member. Because of his crazy eyes (really, his eyes have a insane look), and his crazy insane laugh, and his voice... I really love him, he's fantastic! He is killed by Axel, in the Organization's orders, right after a battle with Sora, in the start of Chain Of Memories, because he defied Marluxia's orders, betraying their plan of taking over the organization, and helped Sora, telling him about the plan to use Namine to control him, and it was really a pity, he was freakin' fantastic! He has the element of ice, and is really smart. he used to work with Ansem, in Radiant Gardens, before he was turned into a Nobody (his name was Even).
His weapon is a giant shield, with some spikes. His death scene is really cool, takes place in front of the mansion in twilight town. I only did not got really mad because of his death, because the one who killed him was my favourite character, Axel. he got along well with Roxas in the start of 358/2 Days, before he was sent to CO.
You can see his Crazy insane eyes in these pictures... they are really freakin' cool, makes he look like a mad genius, because he is really smart in the games, he's the organization's brains. Here's the link to the video showing the battle and his death: http://www.youtube.com/watch?v=hk19pB3MXg4