Uthman radi Allahu 'anhu, because he married the daughter of the Prophet (sall Allahu 'alayhi wa sallam), and when she died he married another daughter of the Prophet (sall Allahu 'alayhi wa sallam). Thus, he was called "dhul Nurayn" which basically means "the one with two lights".

Okay, my question is (I don't know the answer to this one so I hope I can learn something insha'Allah):

What was the name of al Najashi? His title was al Najashi (the Negus), but what was his name? I'm refering to the one who died as a Muslim and the Muslims prayed Janazah for him in absentia.