The term "Master" may refer to several different individuals in the Doctor Who universe.
- The Master is one of the Doctor's greatest enemies, a criminal Time Lord.
- The Master of the Land, sometimes referred to simply as "the Master," controlled the Land of Fiction while the Second Doctor, Jamie and Zoe were trapped there. He later turned out to be a benign author of boy's serial fiction who had been enslaved by a computer, the real ruler of the Land of Fiction ("The Mind Robber").
- "Master" is the title with which K-9 addressed Professor Marius ("The Invisible Enemy") and later the Fourth Doctor. On some occassions, K-9 referred to the Doctor as "Doctor-Master."
- Charles Cranleigh compared the Doctor's skills at cricket to those of "the other Doctor,...the Master," a comparison which makes the Doctor nervous until Charles explains that he was referring to W.G. Grace. ("Black Orchid")