Cunovellasus (The Prodigal Sun)

 was a druid.

One night, as he left the clan to prepare for the winter solstice, he was followed by Calagundus, who was curious about the ritual. At the ruined temple, they encountered the Fourth Doctor and Leela, who helped them scare off the shadow-men who were approaching.

Afterwards, Cunovellasus allowed the Doctor and Leela to join them for their clan's festivities. (PROSE: The Prodigal Sun)