Balthazar Gelt is a character in Warhammer Fantasy. He owns a Pegasus named Quicksilver.
Even before becoming Supreme Patriarch of The Empire's Colleges of Magic, Gelt was very passionate about magic, specializing in the Lore of Metal (Otherwise known as Alchemy). However, he wasn't exactly using it for the best of intentions. The first mention of him mentions that he transmuted lead into gold and then paid a ship to take him to Altdorf, running away before the gold turned back to lead. Of course there was a bounty on his head (Most likely done by the swindled captain. It's still there, funnily enough. Good thing he got a good position).
Anyway, after arriving in Altdorf, he decided to join the Gold College. His passion for science and his natural intelligence allowed for him to become good friends with the Imperial Engineers as well as Patriarch of the Gold Order within a decade. One day, he was experimenting, and that led to a freak accident where something exploded (or not so accidental, remember the bounty). Freak explosion led to some horrible disfigurement (Perhaps his entire skin turned to gold, perhaps it's just boring old scars). Imagine the rage and hatred Settra would spew if he saw Gelt in his golden form, since Gelt got what Settra wanted for countless years due to a accident(but it's unknown if Gelt's golden form actually had living sensation other than just gold covered on the skin like an extra harden shell). Whatever the case, the accident didn't faze him, but instead drove him further to greatness. His power apparently grew enough since that time that he even managed to overthrow the previous Supreme Patriarch (A Thyrus Gormann of the Bright Order).
Since that time, he's just been enjoying being filthy powerful.
It's possible to say that it was Gelt who was responsible in part for the End Times kicking as hard as they have.
Following Volkmar the Grim's disappearance into Sylvania, Gelt built a Wall of Faith around Sylvania, locking in the Undead. He got the idea from one of his apprentices (secretly the Changeling in disguise either trolling everyone or at Tzeentch's request to forestall Nagash's return). Predictably, this pissed off a certain megalomaniacal Vampire Count off royally enough that he had to beg for aid from Arkhan the Black and kick their quest to resurrect Nagash into full-gear.
During that time, Gelt was considered a hero for the wall. See, one day he was met by this weird girl (A vampire under Queen Neferata's thrall) who gave him some strange scrolls detailing a wall capable of melding both faith and magic in a seamless fashion through the prayers of an army of warrior priests and wizards. Not one for knowing modesty, Gelt then attempted to make a bigger one, the Auric Bastion, around the Empire itself so it could be shielded from the incoming invasion of Chaos Vikings. While considered an even greater success, the wall was not flawless, and little chinks tended to appear. The issue was that despite making a bigger wall, he forgot all about the wall around Sylvania, a matter which had to yet again be pushed aside as it became clear these chinks wouldn't fix themselves. During this trip of fixing, he noticed the rise of Valten, the arrival of the undead (triggered by Nagash's resurrection), and the fact that the Changeling had snuck through the Bastion and was ready to cause all sorts of hell. Of these, the last concerned him enough that he decided to keep up tabs with Ar-Ulric Emil Valgeir as the two split paths to trail the daemon.
During this hunt, he also came upon the resurrected Vlad von Carstein, who revealed the nature of the bastion and also exposed a sentiment that the citizens shouldn't have to die if they didn't need to, and to this end, Vlad gave Gelt a book that delved into the contents of necromancy. Despite initially refusing the thought, Gelt did eventually succumb to the lure of undeath and started raising the dead to help him defend the Empire's walls. Since necromancy is considered Heresy, many of his allies began calling him traitor and an unfortunate scuffle saw that Elector Count Adelbrand Ludenhof got eaten by zombies.
Seeking to get away from the place, he lucked out when he found out that Ulric's top priest learned that the Emperor was planning to give Valten Ghal Maraz, and that gave Emil enough suspicion that perhaps the young man was the Changeling and that he'd strike the Emperor during the public meeting. Gelt desperately charged there to convince Karl to not go though with it, but he didn't listen and when guards came to kick him out, Gelt pretty much screwed himself over by raising more undead. At that point, he pretty must just said 'FUCK IT!' and started trying to kill Valten outright until he was held up by Kurt Helborg.
However, it turned out that the Changeling wasn't really Valten, but instead Valgeir, which pretty much broke any faith Gelt had left in himself and so he fled to become Vlad's new minion. He worked with Vlad fighting the Glottkin, but after Vlad was tainted by Nurgle, Balthazar kept away from him and started reassessing his situation.
By the time the final stages came about, Vlad and Gelt finally decided to join the Empire in their defense of Averheim, and during this moment, Gelt managed to bind himself to Chamon, becoming the Incarnate of Metal as he began purging his memories of the black arts. He was the only one who took Malekith's side and said that Nagash couldn't be trusted.
He dies after getting stabbed in the back by Mannfred von Carstein, likely a bit of payback on the vampire's part for caging Sylvania, which leads to the world's destruction. For fuck's sake, Manfred!
Age of Sigmar
The main character of the book "Soul Wars" is a stoic and introverted Stormcast Lord-Arcanum called Balthas Arum of the Grave Brethens chamber, Anvils of Heldenhammer stormhost, who is such a master of the Lore of Metal "it was as if [the winds of Chamon] recognized him somehow". In case you didn't get the hint, the book flat out spells it when Nagash meets him and recognizes him, claiming that he once served him while a world burned and would serve him again and he never takes off his golden helmet , because he needs a barrier between his face and people and likes it that way. He rides a mount named Quicksilver like in WF.
The new Stormcast battletome gave further information about Balthas: His soul was "of another era", and he was so powerful that once he turned a city built entirely of gold bricks into lead.
Total War: WARHAMMER
Gelt is one of the three (for now) playable legendary lord of the Empire as well as the only (for now) lore of metal caster of the Empire. When taken as the factions Head in campaign his stand out attribute is giving the entire faction +10(!) armor. This makes him have one of the most powerful lord attributes by far, despite being harder to start out with due to his inability to corner and destroy enemy generals than the beatstick Karl Franz or allrounder Volkmar. Being a lore of metal wizard, he is good against armored opponent as well as armies known for wearing heavy armor in battle (Warriors of Chaos, Dwarves, most elite monsters or infantries) using his bombardment spell as well as armor debuff spell. He gets a skill tree line in the campaign that allows him to give extra levels to battle wizards recruits as well as decrease upkeep to the artillery in his army. Like the lore, he gets to ride his Pegasus Quicksilver, avoid of all ground danger. In his quest battle, he gets to fought (and maybe kill) his mage rival that tried to steal his seat of the supreme patriarch. Is known for his interesting voice and hammy lines like "DO NOT WASTE MY POTENTIAL."