Battle on the Bridge! Zabuza Returns!

S1, E12: While Naruto concentrates on training to control his Chakra, a mysterious person suddenly appears before him. The person tells Naruto that as long as one has the desire to protect what he loves, there is no limit to becoming stronger. The mysterious figure echoes the sentiment inside Narto and the two feel a sense of connection. But nothing more is discussed between them and the person disappears. Who was that mysterious figure? And for what reason did he approach Naruto?