Tlotoxl

Tlotoxl was the Aztec High Priest of Sacrifice in the 15th century.

Biography
Barbara Wright posed as the reincarnation of Yetaxa. When she called off the human sacrifice of the First Victim, Tlotoxl declared her a false god.

He tried poisoning her with the help of Tonila to prove Barbara's mortality, but failed when Barbara offered them the drink.

Tlotoxl offered Tonila the position of High Priest of Knowledge when the previous High Priest Autloc left for the wilderness.

At the solar eclipse, Tlotoxl tried stabbing Barbara but Ian Chesterton caught him. Ian and Barbara left for the TARDIS and Tlotoxl was able to offer the Perfect Victim as a sacrifice. (DW: The Aztecs)

Behind the scenes
Tlotoxl is very similar in character style to Tegana (in the previous historical serial Marco Polo) - his main role is one of continual destruction of the good intentions of the other characters around him.