Kōga

was the young leader of the eastern yōkai-wolf tribe, or the Yōrō clan, which is 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 with the "useless mutt" about their relative combat strengths as well as Koga's persistent courtship of Kagome.

Although Kōga often flirts with Kagome, it is later revealed that he has promised Ayame, another wolf demon, to make her his wife. Later in the episode, Kōga tries to get Ayame to leave by saying he will only marry someone who can see the sacred jewel shards. At the end of the anime, it is revealed he did in fact marry Ayame. This does not happen in the manga because Ayame is an original character made for the anime, though she is briefly mentioned in the manga.

After suffering serious wounds, Kōga is partially restored by three Shikon shards embedded into his legs and right arm. The shards are eventually taken away from him by Naraku, gravely weakening him; he leaves and disappears from the manga, after telling Kagome that she may leave Inuyasha and come to him at any time. The anime's epilogue reveals that he married Ayame and has become the new chief of the wolf demon tribe.

History
Prior to his meeting Kagome and her friends, not much is known about his past or his parents. It seems that he is the youngest leader of the wolf-demon tribe thus far and he once promised a much-younger Ayame to take her as his wife. This occured during a lunar rainbow, though he later denies that this incident ever occured. It also seems that he has a solid, possibly long friendship with Ginta and Hakkaku.

During the Story
Kōga kills a wolf demon who betrayed him when he came for a hut that belonged to Rin (who later becomes Sesshōmaru's companion).

Personality
Kōga is almost always completely straightforward and his simple and clear demeanor bears no shadow of Magatsuhi. Initially, He had no human feelings, such as the desire to make plans or having concern for the weak. The only exception is with Kagome. Gradually, he does develop a sense of compassion towards humans due to his exposure to Inuyasha's party, mostly through Kagome's influence. His attitude is mostly wild and he is only concerned with survival. He is also keenly in tune with his instincts and will not hesitate to follow them (such as running away when the situation is not in his favor).

Kōga is the young leader of the Wolf-Demon clan. He has the deep trust of his comrades and regardless of the danger he faces enemies on the frontlines of battle in order to protect the pack. He will willingly give his life for the pack. Even if it is a member of the Wolf-Demon clan, he punishes anyone that betrays it.

Kōga tries to protect his comrades at all times. He will punish anyone that hurts his pack, regardless of who they are. However powerful an enemy may be, he will swear revenge. With his pride as a Wolf-Demon clan member, his conviction is unwavering. Koga hurried to the castle to save his comrades. However, all of them ended up exactly as Naraku had planned. It was a battle he faces for revenge. But when Kagura appeared, Koga realized the truth this starts his journey for revenge of the loss of his dead comrades. Ginta, Hakkakku, and some wolves go with him on his travel.

The relationship between Kōga and Inuyasha is sometimes that of collaborator. Since they met, they have been rivals for the love of Kagome. They each realize the power of the other but refuse to admit it. It is just like a cat and dog relationship, but they grow to trust each other little by little. They pursue the same enemy, Naraku, and sometimes exchange information. In a serious crisis, they cooperate with each other.

Kōga rarely makes battle plans. His actions are basically animalistic hit-or-miss. But he sometimes exhibits surprising strategies with his naturally sharp instincts. He correctly aimed the Shikon Jewel shard using his wild instincts on Renkotsu.

As long as he likes something, he is not concerned with the feelings of others. He simply proceeds in one direction. Kōga aggressively told Kagome that she would be happy if she were with him. He approached Kagome forcibly even though they had just met. His expression of love is pure and he goes to meet Kagome wherever she may be. If a woman that he likes relies on him, he becomes elated, forgetting all about combat.

Ayame
Kōga first met Ayame as a young girl after he saved her from a demon. Ayame is the grand-daughter of the chief in the northern mountains. Kōga promised to marry her when she was younger, so Ayame comes searching for Kōga in order to return to the northern mountains and restore balance among the tribes. After Kōga refuses to go with Ayame, she returns back to the mountains alone, and sometime later the two meet each other. In the end of the anime series only, Kōga marries Ayame not knowing that Kagome had returned and married Inuyasha.

Inuyasha
Inuyasha was seen by Kōga as a love rival for Kagome. They each have a name they call each other- Inuyasha is Mutt-Face and Kōga is Wolf-Cub. Although later they do become allies and even view each other as friends(though they will never openly acknowledge it), Inuyasha seems to be the winner of their rivalry since he marries Kagome.

Kagome Higurashi
When Kōga kidnaps Kagome and Shippō only because Kagome can see the sacred jewel shards in the Birds of Paradise, at first. Later in the next episode, Kōga claims Kagome to be his "woman," receiving a slap from Kagome. When Kagome says: " His name isn't InuTrasha, so don't insult him! He's brave, courageous, really good-hearted when he's not being a jerk, and he's got a great name so say it right. Inuyasha." Kōga threatens to kill him once he sees Inuyasha again. During the series, Kōga saves Kagome multiple times while Inuyasha attacks the demon/enemy. Inuyasha tends to get jealous when Kagome is kind to Koga before chasing him off. Kagome thinks of Kōga as a friend.

Sesshōmaru
Kōga met Inuyasha's half-brother in episode 99. Sesshōmaru's companion, Rin, was killed by Kōga's wolf pack before Sesshōmaru brought her back to life with his sword. In the episode Kōga meets Sesshōmaru and they seem to be off to a horrible start when Kōga talks about Inuyasha (being a half demon). However, during the meeting Rin is attacked by a centipede like demon that Kōga kills. They seemed to have a mutual understanding and still it seemed like this confrontation would have turned into a fight if Kōga hadn't have saved Rin.

Appearance
Kōga has blue eyes and black hair that is always tied up into a ponytail with a brown cord. He wears a brown wolf pelt. He has a tail that is like a bushy wolf's tail, which is the same shade of brown, though it is in fact part of his body. Kōga has a brown wolf fur head band, black hair, and he wears silver and black armor. Kōga also has brown wolf fur as shoulder plates. He carries around a sword, entirely for decoration, however he does use it once as a last resort. His ears are pointed and resemble those of Sesshomaru and other demons. He is also usually seen with his posse of wolves and wolf demons, namely Ginta and Hakkaku.

Abilities

 * Whirlwind - Kōga's method of transportation. Whenever on the go, he is enveloped in a high-speed tornado. Despite its effectiveness, Kōga never actually uses it in battle. He usually outruns Ginta and Hakkaku due to his impatience.
 * Strength - In his battle with the Wolf Guardian, Kōga could easily lift the body of the Goraishi Guardian and throw it. Also he has proven to scuffle with Inuyasha, who is very strong, in mere fist fights. In The Final Act, he was also able to hold Inuyasha's Tessaiga with little effort despite being greatly hurt.
 * Jewel Enhanced Abilities- Kōga originally possessed three jewel shards: one in each leg and one in his right arm. These allowed him to run at exceptional speeds and increased the strength of his right arm. He eventually lost all three shards throughout the series, losing the 1st one from his arm at the end of episode 37.
 * Stamina- Being a full-fledged demon, Kōga has incredible stamina. He states that he can run three days without stop and he can fight for a long time even when he is wounded.
 * Endurance- Being a demon Kōga has enhanced endurance. Even when he is seriously wounded he can still fight. In the battle with Ginkotsu and Renkotsu he defeated them even though his legs were badly injured. Another proof of his endurance is then Naraku impales Kōga in the legs and drags him into his own body. While trapped within Naraku, his miasma that could melt forests and mountains failed to melt or even severly injure Kōga.

Weapons

 * Goraishi - A claw that Kōga earns from his ancestor spirits so that he can avenge the deaths of his comrades and destroy Naraku. It creates energy blasts that are equal to that of a fully-powered Wind Scar. The claw shields him, barely, from Naraku's corruption of the jewel but it was only able to protect him once. The Goraishi has literally become a part of Kōga.
 * Sword- Kōga has a long sword at his hip, but he has never used it.This is because his Wolf-Demon clan instincts do not rely on weapons. However this is does not apply to the Goraishi because it has literally become part of Kōga's body.

Trivia

 * Kōga is the only one of the 12 main characters to not appear in any of the movies.
 * Kōga constantly tries to woo Kagome, but to no avail.
 * It was Kōga's wolves that killed Rin.
 * In the Holy Pearl both You Ming and Rou Di based off Kōga and Miroku
 * Kōga is similar in appearance to to Ryōga Hibiki from Ranma ½, who is also romantically interested in the female protagonist and has a similar name that in part means "fang".
 * Because he is a full-blooded demon it's quite possible that he is much older than he looks and quite possibly has semi-immortality.
 * It's quite possible that Koga might be able to shift into a wolf form but it is never shown in the manga or the series.