Atlan is the "Messenger of the Gods".
Messenger of the Gods
This term can be open to misinterpretation and so some clarification is needed. Atlan is not an errand boy or servant of the Gods. He is actually considered to be one of the Greater Gods. The term messenger in this instance is more akin to emissary. For Atlan represents the Gods on matters of great importance and is entrusted with the conveyance of the consensus of the Greater Gods to mortals and Gods alike. His powers of communication are unrivalled.
Some scholars argue that Atlan himself is the Sounder of the Final Horn, depicted in the Southern Skies of Titan.
He is said to have referred to the fact that he also known as the "Ancient King". Given that Atlantis was named after Atlan and at the heart of this lost island was Mount Atlan the volcano it is possible that Atlan first held the mantle as guardian of the realm. The people of Atlantis regarded their king as a direct descendant of Atlan. It is therefore logical to presume that he was seen as the first king of Atlantis. Hence the Ancient King.