End of Time (Symbols of Dooms day) in Lite of Sura Kahaf (Chapter Cave), Harun Yahya wrote this book . Asrar Alam also mentioned in his books i.e. Dajjal volume 1,2 and 3, that the Zulqarnain was a great Prophet/King/Pious Man of Allah who traveled in earth according to orders of Allah and helped poor and victims of the earth. His period may not be confirmed but it is possible there was many Zulqarnains as it is not a specific name of any person but a Knight /designation from Allah used in Koran and Holy Books. It is also described by Asrar Alam that if a Prophet PBUH at any time is in danger and Allah's will wishes to save that Prophet than Allah raise him up while he is living than Allah send him back to this earth for special and important Action against crullers and Satan. So in Chapter Cave (Sura Kahaf) Allah mentioned same topics and subjects of few believers who were slept and awoke up after few hundred years, Zulqarnain also came back after many hundered years and similarly Prophet Jesus (Hazrat Issa a.s) will came back as He was raised up safely by Allah while Jews were trying to kill Prophet Jesus and now the coming of Jesus a.s will be near end of time who will kill the Antichrist. InshaAllah.