Edlin used to train as a Holy Knight apprentice under Howzer alongside his friend Donny. Some time after Donny left training and the kingdom, Edlin did the same. Upon reaching Cant, he joined a band of bandits and stole an egg from a dragon's nest. Using the egg as a hostage, Edlin managed to put the dragon under his command and used it to take control of all Cant. However, since the egg eventually hatched, Edlin replaced it with a replica created with his magic.

(Source: The Seven Deadly Sins: Four Knights of the Apocalypse Wiki)