High Priest was a leader of a religious order.
Dumuzi was the high priest of Ishtar in Kish. (PROSE: Timewyrm: Genesys) Krasis was High Priest of the temple of Poseidon in Atlantis. (TV: The Time Monster) At some point prior to 1430, Yetaxa was an Aztec High Priest. In 1454, Autloc was the High Priest of Knowledge until he was replaced by Tonila, while Tlotoxl was the High Priest of Sacrifice. (TV: The Aztecs) In San Martino in 1492, a High Priest led the Brotherhood of Demnos. (TV: The Masque of Mandragora)
On Exxilon, a High Priest led worship of the Great City of the Exxilons. (TV: Death to the Daleks) One Dalek became High Priest of Florana. (AUDIO: The Elite) In 3885, Hepesh was High Priest of Peladon. (TV: The Curse of Peladon) In 3935, Ortron was Peladon's High Priest. (TV: The Monster of Peladon)