Thordak

Thordak, self-titled "the Cinder King" , was an ancient red dragon, even larger than most other ancient dragons. He and Raishan made the deal to form the Chroma Conclave. With time, Thordak went mad, presumably due to the heart crystal (used to bind him to the Elemental Plane of Fire) that was embedded in his chest. Notably, Thordak killed Elaina (the mother of Vax'ildan and Vex'ahlia). As an NPC, he was played by Matthew Mercer.

Appearance
Vox Machina first saw Thordak in the Elemental Plane of Fire. At that time, Thordak had the standard appearance of a red dragon, albeit an incredibly large and ancient one. On closer inspection, Gilmore could see, instead of the uniform scales of a dragon, the heart crystal in his chest, smooth and jagged and pulsing with power.

Background
Long ago, before maturing into an ancient dragon, Thordak lorded over half of the desert continent of Marquet for centuries. Eventually, he attacked Ank'Harel during its rise to prominence but Thordak was gravely wounded by the city's protector - Devossa - and retreated. He was presumed to have died shortly thereafter from his wounds.

Thordak was not seen again for centuries, until about fifteen years before the events in. Rumors of a powerful drake storming the beaches and seas had been whispered for a long time while ships would be lost at sea. Thordak had survived but was near dead from his fight with Devossa when he was captured by the necromancer Opash who experimented on him in his laboratory on the Island of Viscan in the south of the Lucidian Ocean. These experiments made Thordak more powerful and eventually he destroyed the necromancer. Thordak became interested in Opash's notes and began to make his own additions to them, growing interested in the research into Guuthal the Ever-fed, an ancient black dragon that evaded death by becoming a dracolich. After generations of secretly ruling the Island of Viscan, the dragon (now self-crowned as "the Cinder King") grew greedier than the island's limited resources could satisfy. He began razing the Mornset Countryside, south of the Verdant Expanse and the Stormcrest Mountains.

Reports of a dragon—more massive than any on record—hit Tal'Dorei. At the time, Lady Allura wasn't a part of the Council of Tal'Dorei; she was a member of an adventuring party, much like Vox Machina. Allura's party traveled to investigate, but arrived to find this creature destroying everything surrounding the Gladepools, including Port U'daa and Byroden. (Vax'ildan and Vex'ahlia's mother was killed during Thordak's destruction of their hometown, Byroden.) Gathering a small army of mercenaries, Allura's party hunted the creature back to its new den in the Stormcrest Mountains. They encountered resistance from a large number of lizardfolk, but eventually Allura's forces were overcome by the sheer might of the dragon himself.

Knowing they could not kill Thordak, Allura called upon the Arcana Pansophical, a circle of arcane practitioners that agreed to work together across the lands to keep them safe. They devised a trap that could, they believed, permanently seal Thordak within the Elemental Plane of Fire, preventing him from ever returning to Exandria. They bound Thordak's essence to the Fountains of Creation and thought he would stay there forever. To bind him, they crafted an artifact called a "soul anchor" from the salvaged heart crystal of a primordial fire titan. The heart crystal is an immense gem of pure crystallized ruby and elemental power and energy, fifteen to twenty feet in diameter. The soul anchor crafted from this heart crystal could not be removed from the Elemental Plane of Fire, and Thordak could not escape without the anchor. Although Allura's group succeeded in trapping Thordak, many lives were lost, including three of Allura's companions: Sirus, Dohla, and Ghenn.

During his imprisonment in the Elemental Plane of Fire, Thordak was approached by Raishan. The ancient green dragon had been cursed by a Druid and was slowly dying of a horrific disease. Thordak claimed to know of a cure, (while in reality he knew a way for her to avoid the disease killing her, by becoming a dracolich like Guuthal the Ever-fed,) but refused to share this knowledge with her until she found a way to release him. Raishan propsed a conclave of powerful dragons to aid them and left to prepare - forming the Chroma Conclave.

Raishan's initial plan after infiltrating the Fire Ashari disguised as a human girl, was to release Thordak during the Celestial Solstice. However, the power he was drawing from the heart crystal was making Thordak insane and increasingly powerful. Fearing Thordak would forget the deal in his madness should she wait any longer, Raishan instead initiated the plan during the Winter's Crest Festival.

Vox Machina saw Thordak in the Elemental Plane of Fire while Keyleth progressed in her Aramente with the Fire Ashari. Thordak later escaped to the Material Plane after those events, helped by the ancient green dragon Raishan disguised as a young girl, an outcast whom the Fire Ashari adopted.

Thordak led the Chroma Conclave on an assault against Emon, Westruun, and (presumably) other parts of Tal'Dorei.

Lady Allura and Keyleth revealed through a scrying ritual that Thordak had returned to the Material Plane through Pyrah, devastating the area and killing druids of the Fire Ashari in the process.

As Vox Machina and their allies entered the ruined Cloudtop District of Emon, Thordak sensed their presence and emerged from his burrow.

Thordak attacked Vox Machina and a grueling battle ensued. During the battle, Raishan revealed herself and turned on Thordak, joining the assault against him. After several attacks, the scales on Thordak's chest were chipped away, revealing the crystal within. The Vestiges of Divergence wielded by Vox Machina—the last hit being an arrow of dragon slaying loosed by Vex'ahlia—cracked and shattered the crystal, causing Thordak to shrink down to Raishan's size—still a very large dragon, but much smaller than he was before. Realizing the danger he was in, Thordak turned and dove down into his burrow. However, Vax'ildan swiftly chased the dragon into the hole and dealt the killing blow with Whisper.

Raishan took Thordak's corpse with her as she escaped from the red dragon's lair.

Relationships
Thordak and especially Raishan established a loose alliance of dragons known as the Chroma Conclave, which also included:
 * Brimscythe
 * Umbrasyl
 * Vorugal

Abilities

 * Fire Breath (DC 24).
 * +16 Constitution saving throw.
 * +12 Strength saving throw.

Trivia

 * Matthew Mercer revealed during that both Thordak and Brimscythe wanted Emon for themselves. Thordak had originally planned to kill Brimscythe quietly, without the other Conclave members knowing. However, Brimscythe was instead slain by Vax'ildan (who, coincidentally, would later slay Thordak during the liberation of Emon). Thus, Thordak's claim to Emon was uncontested.
 * The eggs in Thordak's lair were indeed laid by Thordak. The soul anchor embedded within his chest mutated his body, eventually allowing him to reproduce asexually.
 * In the Critical Role Major Arcana Tarot Card Set, he represents "XIII - Death".