Who is Jinn from American Gods and what is their importance?

The jinn tells Salim that people do not believe anymore. When Salim gets out of the cab, he gives the jinn his room number. The jinn comes to Salim and they have sex. When Salim wakes up, he finds the jinn has switched lives with him, and left him all the cabdriver's id and license. Salim takes up the driver's job, happy to have a new life.