A vizier was a high-ranking advisor to a monarchy in some Eastern cultures. The Doctor encountered several viziers, both on and off Earth.
In the 9th century, the Fifth Doctor encountered the Sudanese vizier. (AUDIO: The Destroyer of Delights)
In 1289, the First Doctor encountered Kublai Khan's vizier at Khan's palace. (TV: Marco Polo)
While in Paris in 1626, Erimem told King Louis XIII that the Fifth Doctor was her vizier. (AUDIO: The Church and the Crown)
The Third Doctor encountered the Sclaponian Grand Vizier. (PROSE: Island of Death)
The Eighth Doctor encountered the glass Vizier of Fortalice. (PROSE: The Scarlet Empress)
In 2593, Bernice Summerfield encountered an individual who called himself the Vizier, whilst on Perfecton. (PROSE: Oh No It Isn't!)