Milgasia is known to be the leader of the remaining golden dragons who were originally in the service of the Water Dragon King.

Upon entering the Valley of Dragons, Lina Inverse and company are found by Milgasia. He aids Lina by taking her (and, in the anime, Martina Xoana Mel Navrachoa who tags along) to see the real Claire Bible so that Lina can learn the truth behind the Giga Slave. Later, in the novels, Milgasia and his elven companion Mephis also join Lina in her travels for a while.

Milgasia probably is over a thousand years old as he seems to have first hand knowledge about Xellos and the War of the Monster's Fall. At first, he is worried about Lina and company's association with Xellos, until Gourry (in a typical idiot comment on Xellos's age) allows him the chance to realize he doesn't need to worry about Xellos's influence, since this group is completely not intimidated by Xellos in any way.

Milgasia's first appearance is in episode 20 of Slayers NEXT, which roughly equals the seventh novel and manga issue.