Yerma was a Bukolian official. He met both the First and Sixth Doctors when they came to Bukol.
Yerma was called in when the First Doctor's visa image didn't match his appearance. The Doctor eventually convinced Yerma he was who he said he was, and Yerma helped him find his missing companions Steven and Dodo. He also found the unconscious Sixth Doctor, who had been attacked by Mykloz. (PROSE: The Golden Door)