Riku is a life-long friend and rival of Sora, Riku is from Destiny Islands and is a childhood friend of Sora and Kairi. He is a calm, cool, collected teenager who is not afraid to push the boundaries. Riku has a strong competitive streak. He shows his competitive side when he challenges Sora, saying that his heart is stronger than his friend's. Riku is a tall and muscular teenager with pale skin, bright blue-green eyes and silver hair.

Spoiler

Due to the influence that Maleficent has on him, Riku also becomes increasingly jealous of Sora. When he realizes that Sora has acquired new friends in the form of Donald and Goofy, Riku feels that he has been replaced. His jealousy grows when he learns that Sora owns a Keyblade. This jealousy results in numerous fights with his former friend throughout Kingdom Hearts, and opens the door for Ansem, Seeker of Darkness to possess him. He eventually snaps out of it and feels tremendous guilt and remorse for all he had done.

(Source: Kingdom Hearts Wikia)