Abner. He was from my home-brew world. He was a gold dragon that often appeared in human form (and Abner was his human-form name). He was often a guide and mentor for the player characters. In my world the main threat was Zermarx, a mighty necromancer under Orcus who was waging a war against the PCs kingdom after they released him. It was Abner who had imprisoned him after the last war and then built up defenses in anticipation of Zermarx's inevitable return. Abner was a fumbling wizard prone to having his spells go astray, such as the occasional fireball that would land in the middle of the party.
If any of Abner characteristics sounds at all familiar it is because I blatantly stole the ideas from Dragonlance and Fizban the Fabulous. My players had not read the books so I was free to pillage ideas and I liked the concept of a bumbling mage that was a random element with the party.
As time wound on Abner slowly changed from a bumbler to a competent quest director. However, he is my favorite D&D NPC because...
A) He was fun to play as I tried to come up with some outrageous antics he could perpetrate.
B) The players had fun interacting with him.
C) He was an excellent quest guide.
However, he is not my favorite NPC of all time, as that belongs to Hugo, from my Feng Shui game. Hugo is a demon conjured by the Eaters of the Lotus that the player characters befriended. But that is a post for another day.