Roxas was created when Sora stabbed himself with the Keyblade forged from the hearts of six of the seven Princesses of Heart and became a Heartless at Hollow Bastion to release Kairi's heart. Roxas at first, thought he was from Twilight Town until towards the end of his summer vacation. Roxas resembles Ventus since Ventus' heart merged with Sora's.
He was originally a member of Organization XIII as their thirteenth member and was able to wield dual Keyblades. He was Axel's best friend before he lost his memories.
Roxas was born in Twilight Town and was soon discovered by Xemnas who gave him his name and introduced to the Organization by it's leader Xemnas. Being half of Sora, (who is the carrier of Ven's heart) Roxas was able to wield the Keyblade. Roxas befriended Axel another member of the Organization.