Who is Hizdahr from A Dance with Dragons: A Song of Ice and Fire: Book Five and what is their importance?

Hizdahr zo Loraq, Fourteenth of that Noble Name, King of Meereen, Scion of Ghis, Octarch of the Old Empire, Master of the Skahazadhan, Consort to Dragons, and Blood of the Harpy is Daenerys' husband. Their marriage is one based on convenience and political advantage.