In Sahih Bukhari - Volume 9, Book 89, Hadith Number 329 - Jabir bin Samura RA narrated (mafhum):
"I heard the Prophet (SAW) saying, "There will be twelve Muslim rulers (who will rule all the Islamic world)". He (SAW) then said a sentence which I did not hear. My father said, "All of them (those rulers) will be from (the) Quraysh."
The most appropriate interpretation of this Hadith is that it refers to twelve leaders who will come until the Day of Qiyamah. Some may have already passed and the others are still to come. Moreover, it is not appropriate to specify any names when Nabi Muhammad SAW himself has not specified them.
(As based on the grand kitab providing the explanation on Sahih Bukhari - Fathul Baari)