Sora Inoue
Sora was Orihime Inoue's older brother. He raised her for most of her life, and died in the Kurosaki Clinic from wounds suffered in a car accident three years before the series began. He enters the story quickly as a hollow, Acidwire. In the anime, he is seen being dragged to Hueco Mundo to be turned into a hollow at the behest of Grand Fisher. This is not shown or even suggested in the manga; one can assume that his feelings of being forgotten by Orihime were what prompted his transformation in this case.
Acidwire
In the official English-language manga translation, he was given the name Kakei as his real name had not been mentioned at that point,but he is still called Sora in the character popularity polls. Curiously, before being purified by Ichigo, Sora was able to remove his hollow mask and recover his original personality. While such an act has been described as the process which creates an arrancar, Sora remains in hollow form, albeit with a human head. Presumably, this is because of Sora resisting his hollow self, rather than the hollow itself removing the mask.