Roxas

Ranked as XIII in Organization XIII. His and Xion's absense in the Organization resulted in the need to recruit an additional nobody to wield the Keyblade.

Key Plot Points
Roxas is defeated before Mandroxa or any of the other newer members join Organization XIII.

Demise
Roxas was absorbed by Sora so that he could awaken with his returned memories. Roxas is the only organization member to lose his body but not fade away completely.