The vizier was the highest official in Ancient Egypt

Ancient Egypt

Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

  to serve the king, or pharaoh

Pharaoh

Pharaoh is a title used in many modern discussions of the ancient Egyptian rulers of all periods. The title originates in the term "pr-aa" which means "great house" and describes the royal palace...

 during the Old, Middle, and New Kingdoms. Vizier is the generally accepted rendering of ancient Egyptian tjati, tjaty etc, among Egyptologists. The Instruction of Rekhmire-(Installation of the Vizier

Installation of the Vizier

The Installation of the vizier, alt. Instruction of Rekhmire, Regulation laid upon the vizier Rekhmire, is an ancient Egyptian text dating to the New Kingdom found in Rekhmire's tomb at Thebes...

), a New Kingdom text, defines many of the duties of the tjaty, and lays down codes of behavior. The viziers were often appointed by the pharaoh, most from loyalty or talent.
The viziers were appointed by the pharaohs, but often belonged to a vizierial family.