Mogadon attended the Thor'sday Thursday festivities on the Isle of Berk, representing the Meathead Tribe as well as to watch his son during the Final Initiation Test to become a Viking of the tribe. He placed bets with Stoick the Vast on which boy would be announced as the "Hero of Heroes". However, when the Viking Initiates' dragons run amok, he was included in an Elder Huddle to decide their fate. During the huddle, he got into a fight with Terrible Tuffnut.
- "The Elders consulted for a long time. Mogadon got angry at one point and swung a fist at Tuffnut. A twin held on to each of his arms until he calmed down again."
- ―Book 1
Since the initiates failed to demonstrate control over their dragons, the Elder Huddle decided to exile all of them, even Mogadon's son, Thuggory.
Mogadon is a large Viking with a patch over his right eye and a missing left leg. He has a peg leg in its place. He has a beard that appears to be curly and fluffy.