Garlin Munn was an Armidian scientist.
He was one of an exploratory research group who came to Scotland on Earth around 2000 BC to find out about Earth's inhabitants, minerals and fauna. They set up a collection of data collection reservoirs that blended in with the area's stone circles. The party of ten was ambushed by tribal human warriors. Six of them were killed, and the remaining four were left for dead. They were placed in healing capsules underground along with the Tharon stone.
After being awakened by roadworks in the 1970s, they shot down an RAF fighter jet to examine it and forcibly questioned the pilot Frank Parry about the planet's military capabilities, but this process damaged his brain. He rescued Mike Yates from being atomised by an energy packet that was launched from the Easter Aquhorthies stone circle and took him to the house near Portsoy and tried questioning him, as he was not as angry as Parry. The Third Doctor informed the group that Tharos had been destroyed millennia before. Yates broke free and Sergeant Benton opened fire on the Armidians as they escaped, killing one of them. To protect the last of their kind, Garlin decided to kill the aggressor humans on Earth with the Tharon stone and make Earth the new home for the Armidians. The two Armidians at relay points were killed by UNIT teams led by Benton and Brigadier Lethbridge-Stewart, and Yates and his team earthed the Tharon stone with some wire fencing, rendering it powerless. The Doctor survived a murder attempt by Garlin, but was unable to save him. (AUDIO: Vengeance of the Stones)