The Aztecs was broadcast in four parts in 1964. The Doctor and his companions arrive in 15th Century Mexico during the Aztec Empire, where Barbara is believed to be the goddess Yetaka. She embraces the role because she wants to persuade the Aztecs to abandon human sacrifice, though The Doctor warns her of the dangers of trying to change history.
Sacrificial priest Tlotoxi (John Ringham) is a bloodthirsty advocate of human sacrifice and does not believe she is Yetaka. He is quite frightening and repulsive. Ian has been forced into the military and there is a plan afoot to kill him in battle. Tlotoxi attempts to poison Barbara to prove she is mortal. Susan refuses to marry the next sacrificial victim, which is her role as a temple virgin, and is scheduled for sacrifice herself. And The Doctor finds himself betrothed to an Aztec woman when he shares a cup of cocoa with her.
The Aztecs is considered one of the great Doctor Who stories, and it has survived completely intact. It was a great success as well on VHS and DVD. The scary and creepy Tlotoxi was extremely popular. Ringham was told, "Make all the children hate you," and he did. He got his own action figure in 1998.
Part 1
Part 2
Part 3
Part 4