The TARDIS Databanks: Online

Biographical Name      Classified
Aliases      The Master, Koschei, Professor Yana, Harold Saxon
Homeworld      Gallifrey
Profession      Time Lord
Born      Unknown

Physical Species      Gallifreyan
Appearance      Anthropomorph - Least Weasel
Gender      Male
Height      175 centimeters (5 feet and 9 inches)
Weight      66 kilograms (10 stone and 6 pounds)
Fur Colour      White
Eye Colour      Black

Notes Voice Actor      John Simm
Regular Attire      A black suit jacket, a white long-sleeved shirt, a black
     tie, a pair of black trousers, and a pair of black shoes.

Incarnations The First Master
African Lion
Roger Delgado
The Second Master
Lappet-faced Vulture
Geoffrey Beevers
The Third Master
Spotted Hyena
Anthony Ainley
The Fourth Master
Lace Monitor
Eric Roberts
The Fifth Master
Polar Bear
Derek Jacobi
The Sixth Master
Least Weasel
John Simm