Senegos

This is the first world NPC I can recall as having more than one billion HP. Interestingly, this is denoted in game as 1.2G (yes, "G"). I refer to this as 1.2 gigahealth -- or for those that like rounding for the sake of classic time traveling movies featuring Michael J. Fox, 1.21 gigahealths.

Edit: The 8.0 stat squish has bumped Senegos' HP back into the millions.

Click-poking Senegos, you get:

"Though I am weak, I will do what I can."
"The blue dragonflight is but a shadow of its former glory."
"I am the oldest of my kind."
"Though I am weak, I will do what I can."
"I believe we can help each other."
"Come closer, little one, my eyes are not what they used to be."
"Must you act like a child?"
"Have you no respect for your elders?"
"I can use MY frost-breath more than three times a day, you know!" (ref. D&D Monster Manual entry on blue dragon breath weapon abilities)
"In all my millennia, I have never met one as IMPERTINENT as you!"
"Get off my lawn--er, ISLAND!"

A clue to the origins of his name might be related to the Latin word "Senex".

Senex is a term that refers to an old individual, and given that Senegos is hinted to be an incredibly old dragon, this makes some sense.