Brelarn was the Warlord of the Zygons. He and a group of Zygons crashlanded on Earth around the start of the 20th century with two Skarasens.
He served as their commander during their plot to defeat the Human-race and turn Earth into a new Zygor. Some of the Zygons felt this was too risky but he felt the risks needed to be taken. He personally thought up their conquering scheme. He kill King Edward VIII at when world leaders attend his funeral they would capture them and take their Body Prints. Brelarn took the form of the dog Teazel and mauled three Zygons to death for mutiny. After Teazel escaped his form changed back to Zygon. He attempted to stop the Doctor subduing the Skarasen. The Skarasen sighted his master and in anger ate him whole. (TDA: Sting of the Zygons)