The Longest Journey Edit
The Old God dwells in a chasm at the bottom of the Great Sea in Arcadia. He is worshipped by the Maerum as a "god who fell from the sky", and, according to the murals in the Maerum's abandoned temple, is the member of the Draic Kin who brought the Maerum and Alatien to Earth.
The Old God is the largest of the Kin: we never see him in his entirety, but his eye alone is as large as April is tall, and his titanic form breaks the surface of the water when he takes her to the Dark People. He offers April a great deal of useful information, including the location of the singularity that leads to the Guardian's Realm. He also mentions the 'Day of Ascension', when the Draic Kin will return home, but doesn't elaborate, saying only that it will not be for a long time and not everything is ready yet. He answers April's question of 'Who am I?' by telling her that her journey began with an answer, and it is only now that she knows the question.
Although he is worshipped by the Maerum, the Old God is also served by the mysterious, seafaring Dark People, ordering them to prepare a Star Map for April and to take her to Marcuria. It seems likely that the Old God is the most senior of the Kin, as he commands authority and is clearly possessed of powerful magic, but his only interest now seems to be resting until the Day of Ascension.
Ten years after April's journey, something has begun hunting the Draic Kin: an enemy that is "not mortal" according to the White Dragon reborn. The Old God has apparently fallen victim to it, because she cannot hear him any more. This does not seem to have affected the Dark People, and their Library remains a sanctuary, but April is surprised and unnerved to hear this news.
However, there is no evidence that the Blue of the Kin is actually dead. According to the White Dragon, he has only "gone silent".
The appearance of the Old GodEdit
Compared with the other Draic Kin on Earth, the Old God's appearance is much less lizard-like and more undefinable.His first and actually clearest depiction in "The Longest Journey" is on the mural near the Ancient Shrine (compare second picture on this side), where he looks rather bug-like, with six fins and the one eye. In some respects, it can be compared with the one-eyed pyramide on the crystals from this cave. But since this depiction is very old and in religious context, it might be more abstract.
When April is finally allowed to talk with the Draic Kin, she actually encounters a hill-like object, burried in the sand. During the cut scene, there can be seen a blue head with white markings, which might form his face, inside of this object.
April then is allowed to enter the object where she finds a giant eyelid like on the mural.
The last time we see the Old God he carries April to the surface, but through the darkness and the movement we still can't make out much of his body. However, there is promotional material for The Longest Journey that depicts a giant beast with crusty shell and six fins, that bears a big resemblance with this moment.
In conclusion, the Old God's lizard form might be in many respects true to his identity and his enviroment: a thick outer shell with a mighty spirit inside, both rather inscrutable; designed to outlive the ages and the tides of the ocean; with no need to move or react to the turns of time, unless it's inevitable.