Bubbles is the only one of the elder dragons not to have been named in any way, we've seen Kralkatorrik burn the Dragonbrand across the land of Ascalon and he is assumed to be lurking somewhere in the far north of the land, Primordius has awoken his Destroyers and is tearing into the stone dwarves deep below the surface of Tyria, Jormag and his Sons of Svanir are terrorizing the Far Shiverpeaks, and of course Zaitan is eating dirt after getting a heavy dose of cannon fodder to the belly. Some of these antagonists have had cameos in the novels - most notably Kralkatorrik in Edge of Destiny.
But Bubbles has remained a relative mystery. We know that his awakening has forced the krait, largos and quaggan out of their deep-sea homes and into shallower waters around Tyria. However, one crafty Redditor has also been able to take a guess at his name: