Dreaded Day 13…I will have to say I do not have a Most Memorable Character Death as a player.. but as a DM.  I was running the Return to the Temple of Elemental Evil. The encounter that followed overshadowed the rest of the game so greatly that I to this day do not recall what the last epic fight is at the end of the adventure.
But before I can tell you the story I have to introduce the man. Zod
Zod was a Paladin, Plagued by visions by his god. He was destined for great things deep down but on the exterior it was a marvel that he was even a Paladin. Zod was a Terrible drunk. When in a city or town as much of Zods coin that went to the church also went to the closest Tap house. Zod drown his visions in cheep strong ale any chance he could.. But when it came time for work Zod took his roll as serious as his drinking. Zod would not drink on adventures. And he fought evil with a passion few could match. Zod. At the start of any combat or potential encounter Zod would begin with Detect Evil. If he did indeed detect evil he would draw his blade Don his shield and wade forth with a simple cry of “I Smell EVIL ! ”
As the party grew in size and gained level Zods roll changed form one of the front line combatants to protecting the cleric at all times.. If she moved up he flanked her and defended her. If she hung back he would fight near the front but always was the member of the group to fade back and keep anything off of the cleric. So Zod became Zod the Stalwart Defender. At that time Zod actually began tacking blows for his cleric to defend her from attack. Zod would lay his life down for those that he believed in.

And so as the adventure of the Returned to the Temple of Elemental Evil began to draw to a close.  The Death of Zod.

My group was Deep into the story at this point and the final battles were fast approaching.  As the Party entered the ground floor of the final tower before them. They face off with a well prepared ancient Red Dragon.  The fighting was fast and furious I was determined to not pull my punches that day. And with two NPC’s in the party someone was going to die. As the group pushing 8 players with the NPC’s.  2 Paladins 1 Barbarian 1 Cleric 2 Wizards 1 Rouge & a Samurai.  In the first moment of the combat the Dragon took the Rouge out of the fight with a brutal attack. Scooping up the Rouge in its mouth and using his breath weapon.. DONE.. Not dead but wishing they were. The Samurai was tail slapped into a pit trap of mud that instantly turned to stone imprisoning him from the waist down.
The  players began to find chinks in the beasts armor and cut him down much faster then he was able to handle. The Dragon was intelligent and had taken notice that the party had two Paladins in the group. So I as a DM had a plan.. and this is how it went down..
When the fight was drawing to its end and it looked certain that the Dragon was going to be defeated I had planed for the dragon to Feign surrender. .. Little did I know that they would Knock the damn thing to 1 HP !!! So I had to make it good.

The Dragon Roars Paladins I call for Mercy, Parlay!! I have lived too long to die in this pit. Take what you will and go.. I will fly you to the chamber above if you just let me live… And they stopped. To my shock and the RAGE of the samurai the party stopped ! He is convinced this is a trick .. He declares that he is attacking the dragon.. he rolls triple Nat 20s.. !!!!  The party his half erupting with cheer and shock.. And then I steal the moment and the emotion from the room in one breath and say. As you throw your blade. Zod having given his word to parley.. Declares the dragon his defense target and steps between your blade and the dragon as it is about to strike.. Impaling Zod and he falls Dead..
The stunned silence was deafening .. The tears started.. Cleric and Paladin called for God rolls in an effort to save their fallen comrade.. Certainly their god would intercede and save this good man whom had daily visions !  (home-brew rule. 1-3% on D100) Both the cleric AND the Paladin roll a Nat 1!!!!!
A pillar of light centers on the Dragon and the Fallen warrior. The dragon shape shifts to take on the form of a human and scoops the fallen zod up in her arms. She Dons His Shield and swords. Raises her blade to the heavens and Swears to follow their god from this day forward as a Paladin in the name of Zod.
The Stunned party watches as the dragon nods to them scoops up their fallen companion and informs them she will meet them at the town nearby after she sees to Zods Burial.
Almost 10+ years later I still have the Paladin Dragon make occasional NPC cameos.