The knowledge about the famous Dulo clan, the ruling dynasty of the Bulgars (that is to say during Old Great Bulgaria and the First Bulgarian Empire), is up to now quite insufficient. Nominalia of the Bulgarian Khans was for a long time the only known manuscript, where names of seven rulers of the Dulo clan are listed without any probably blood relations between them. In this book the genealogy three of about 870 rulers of the Dulo clan and more than 40 dynasties during a very long time period until the begin of the 17th century are presented.

The branches of the Dulo clan in following countries are considered: Idel, the Hun Empire, the Turkic Khaganate, Old Great Bulgaria, Kara Bulgaria, Khazaria, Hungary, the First and the Second Bulgarian Empire, Volga Bulgaria, the Kievan Rus' and the Russian principalities incl. the Muscovite Rus'/Russia.

According a hypothesis, the brothers saints Cyril and Methodius are also descendants of this famous clan of rulers.

The genealogy tree of the Dulo clan is created by the author and the biographies of the rulers content only citations of the used bibliography partially in Bulgarian, Russian and English language.

As by a wonder, like the mythology bird phoenix, a lot of long believed lost information about the Dulo clan, as well as about the ancient Bulgarian history, comes again to light to show a common and grand image of it.

The second edition of the book consists of two volumes (Volume 1 is edited in two variants – in English and in Bulgarian, but only the Bulgarian variant contains also the respectively part of the biographies).

The book does not have a pretension for exhaustiveness and is an unconventional trial to bring some order, structure and clear arrangement not only according the insufficient researched genealogy of the Dulo clan, but also to illumine the sunk in oblivion old and medieval Bulgarian history, as well as to some degree also the history of other nations, which had points of contact with the Bulgarians and their ancestors.