Necromunga

The official story is he passed in the final battle taking the kings with him. This is only partially true. While he sat using his magic to heal up his injuries, one of the people assigned to escort him lopped off the fallen king's head as proof to show they were victorious. He protested such an action as it was wholly unnecessary as with his magic, they easily could've shown the corpse using magic to end the fighting. The armor-clad man merely shrugged stating "what's done is done, but things were still not complete. There were loose ends to tie up." He turned his head finally noticing that king's child cowering from the sight before him(?).  Snapping his head back to the man, a scowl on his face as he moved himself between the man and the child, leaving a trace of magic in the corpse of the king before moving away from it. "We did what we had to come here for, no more blood needs to be spilled." This buffoon didn't help him fight and now wanted to harm a child.

His magic reserves were low from maintaining his litany of active spells/effects(buffs/debuffs) the issue only made worse from having just finished healing himself. "Not much of a choice, huh? Kid, there's a silver haired elf out there named Esta and say Reol said Ortha-ro and point to yourself." The child opened his(?) mouth to speak and vanished much to the armor-clad man's rage. The vitriol that spewed forth told the man raised by elves all he needed to know. This man only wanted to slaughter elves and if he was allowed to leave this room alive, he surely would target noncombatants if there were any inside the stronghold. Magic near zero, he needed to deal with this guy before it got out, he helped what's likely the prince escape to safety, but that wasn't the only thing he needed to make sure, he needed to find out the truth behind this war. Clutching what remained of his sword, a smirk grew across his face. "You're a pretty loud mutt, aren't you?" A blinding light emanated from the shattered sword, a mindwipe spell erasing the past 30 minutes from the man's mind.  

This unfortunately also erased the order to not harm him until victory was assured from the armored man's mind. Without a second thought, he plunged his sword through the mage's back, but he didn't stop at just one. He continued even well pass his death and cut his head off. "Scum like you need to be wiped." He spit on the corpse before him as he opened the oil jar. Dumping the oil, he spat his hatred for all who share a similar feature to the mage, pink hair and/or red hair as well as the dark elves and those he deemed unfit to be among knights. He lit the match and unceremoniously dropped it on the corpse before walking out of the room, the fire spreading and the tide of the battle outside having completely changed. The army which was bolstered by the mage were falling left and right, the undead under his control attacking ally and enemy alike, those raised by him merely walking away from the battlefield killing any who tried to stop them. The battle went from a near even match to totally one-sided. He couldn't understand why as he fought his way to the leader, but never made it as he was grabbed just feet away and torn in two by one of the undead before he could make it to him to proudly proclaim he did what the king wanted.

The army of 34,000 only returned with a total of 150 after the battle. Reinforcements came for the dark elf stronghold and those who escaped were barely able to do so. They knew from what their observers saw, four of the kings were killed, but so was the mage who was integral to their victories. They didn't need to know he fell to know why they lost. They were able to detect teleportation magic but couldn't trace its origin or its destination. They assumed someone far more powerful teleported in and killed their mage. The king frustrated decided to pass a story of the mage dying so those who lived can return to their families and painted him out to be a martyr to bolster the people's faith in him and the war he waged solely for the mines in the dark elf territory. The tale he spun was of the mage facing the four kings and a horde of undead with dark elves alone while protecting the injured. he spoke of how he took a fatal injury to save one who was about to be a father and passed with a smile on his face knowing a child wouldn't grow up without their father. He was sick of paying a portion of the proceeds to them, his kingdom owned the land around the mines, they should be paying HIM, but his weak father let them walk all over him. "He believed we would win; we mustn't disappoint are heroic mage!" He rallied the people to fight a war he started out of greed, the subject of his tall tale's ashes blowing in the wind.

300 years later, the kingdom won only due to the efforts before his passing. The elf, now alone working in a magic shop keeping a rather low profile. The elf thought back to the child she raised and what she told the kid everyday "It was his wish you live a safe life. He might act scary, but he's such a softy, especially when it comes to pretty girls like us." On the child's hundredth birthday she added to the responses, "They say he's gone, but he's not. He's too much of a pest to die." A ghost from the past walked through the market. The man who became a martyr... the mage who to the world went by Necromunga, but to those two elves, "the king of poor spending habits", Mana Lore.

Notes:

1. Mana can swap between male and female and does it to justify the shitty spending habits.
2. Mana couldn't before that fight and doesn't really care how/why it's now a thing
3. Mana finds crossdressing as a relaxing hobby and kind of fun... mostly because of how much it pisses off the Elf friend.
4. Mana was once tied up and hung from a tree and used as a punching bag by said elf for calling another elf who he's also friends with, an anvil