Koga (鋼牙 Kōga?) is the young leader of the eastern wolf-demon tribe, who was nearly wiped out by Kagura and Naraku. He first meets Inuyasha as an opponent in battle, but becomes a reluctant, occasional ally despite maintaining a strong sense of rivalry about their relative combat strengths and the courtship of Kagome. He quickly falls in love with Kagome after kidnapping her because of her kindness and beauty. Inuyasha is always uneasy and jealous during Koga's visits because he worries that Kagome might have feelings for Koga. In this way Koga has often been the source of Kagome's and Inuyasha's fights.
Koga later wields a most powerful weapon named Goraishi and carries a sword that he does not use often, which he took from a human as "decoration". After suffering serious wounds, Koga is partially restored by three Shikon Jewel shards embedded into his legs and right arm. The shards are eventually taken away from him by Naraku, gravely weakening him; he is last seen telling Kagome that she may leave Inuyasha and come to him at any time.
In the epilogue of the anime, it is revealed that Koga united all of the wolf demon tribes and married Ayame, the wolf demon girl he had long ago promised to marry "on the night of the lunar rainbow," a promise he had seemed to have completely forgotten when she appeared earlier, but evidently eventually had to keep.