Milgazia in his human form.
Milgazia (Japanese: ミルガズィア Romaji: mirugazia and known as Milgasia in the English dub) is known to be the leader of the remaining golden dragons who were originally in the service of Aqualord Ragradia. He is voiced by Masaaki Ohkura in the original Japanese version and by Zeke Zeigler in the dub by Software Sculptors.
Milgazia in his true form.
Upon entering the Valley of Dragons, Lina Inverse and company are found by Milgazia. He aids Lina by taking her (and, in the anime, Martina Zoana Mel Navratilova who tags along) to see the real Clair Bible so that Lina can learn the truth behind the Giga Slave. Later, in the novels, Milgazia and his elven companion Memphis also join Lina in her travels for a while. During this arc it is revealed that Milgazia actually lost his right arm in the Kōma War; he created a prosthetic limb using magic that can be detached from his body but otherwise functions just as well as his other arm, to the point that even he himself often forgets about its existence. This prosthetic changes shape with him when he assumes a human form.
Milgazia is probably over a thousand years old as he seems to have first-hand knowledge about Xelloss and the aforementioned conflict.
Milgazia's first appearance is in episode 20 of Slayers NEXT, which roughly equals the seventh novel and manga issue.