Tannis is currently the leader of the Gold Draconium Dragon Priests and is one of Connor's closest allies within the Ancient Order of Priests as well as being the Priest who speaks to the Dragon Booster in place of all the Priests. He was also the priest who trained Connor Penn and Word Paynn in the ways of the Priesthood. Artha Penn's middle name is Tannis, named after this character.
Tannis played a large role in helping Connor succeed in breeding back a gold draconium dragon, with the details elaborated on in Episode 0: The Alchemist. Not much else is known about him except that he is not entirely strict as the Priesthood would like him to be, and at some point when he was young, rebelled against them just as Connor did to create a new Beaucephalis. He also acted outside of the Priesthood in giving Connor the knowledge he needed to successfully breed Beau as well as gain the lost Gold Draconium gauntlet of the Dragon. From interviews with both of the series' writers, there was a live action Dragon Booster movie planned where Tannis was going to star as the main character, and his story told through it.