Near was raised in an orphanage, and is highly intelligent. Watari was the owner/creator of this orphanage, and due to this all the children in there are highly intelligent, but Near was always at the top. Because of this, Near was chosen as one to possibly precede L if anything happened to L.
Near figured out many of the details on the Kira case that L didn't find out until it was too late. Due to this, the president of the USA makes Near the leader of an organization that is focused on finding Kira. As with L, Near has no written proof of his real name or any photo's anywhere