Much like humans, the vampires also followed a social hierarchy construct, albeit theirs was a bit archaic.
However, unlike humans, their society is based on power. So, in a sense, their titles are also a symbol of the strength they possess.
For example, Common Vampires are the least feared and less powerful. Above them are Noble Vampires. They are ruled by Seven Vampire Kings. And the one who rules them all is the one who was in slumber for the most part of the novel— The Vampire Monarch.
Most of the Noble Vampires are elite soldiers of the vampiric army.
These abominable fiends are seen as the Harbingers Of Death and for a very good reason. After all, they are the second most dangerous beings their species has at their disposal currently.