Gō Koga (古賀 剛, Koga Gō) is a large and muscular man who resembles a punkish biker with spiky orange hair. Even without using his doll, Koga has impressive physical strength, able to easily overpower Ichigo with just his bare hands. His doll is Dalk, a female metallic doll who can control her molecules and reshape herself at will. According to episode 83, Koga's real name is Claude Gauguin, and he lived in a European country in years past. He has lived for over 12 generations. After a falling out with Kariya over his plan to destroy Soul Society, which Koga found too extreme, Koga attempted to find and stop Kariya himself. He ended up fighting and losing to Tōshirō Hitsugaya instead, as neither he nor Dalk could contend with the extreme cold and long-range nature of Hitsugaya's Zanpakutō. He did not die, however, and was secretly taken by Yoruichi Shihōin to Rantao's home, where he was nursed back to health. Upon discovering that he was the last Bount, he apologized for the actions of his race, and Kariya in particular. He was last seen living with Rantao. No mention is made of Dalk's fate; however, considering that Bount are supposed to die with their dolls, it can be assumed that she either still exists in some form, or that Koga is merely an exception to conventional Bount rules, like Yoshino.

Source: Bleach Wiki