Cerkonos

Cerkonos is the headmaster of the Fire Ashari in Pyrah, and one of the guardians of the portal from the Material Plane to the Elemental Plane of Fire. As an NPC, he is portrayed by Matthew Mercer.

Background
Not much is known about Cerkonos. As headmaster of the Fire Ashari, he likely completed an Aramente earlier in his life and may now have a greatly extended lifespan as a result.

Keyleth's Aramente
Cerkonos led Keyleth through the fire trial of her Aramente.

Pyrah's Destruction
At some point near the time Thordak escaped from the Elemental Plane of Fire, Cerkonos lost his left arm.

Sealing the Rift
Cerkonos led the Fire Ashari's efforts to close the rift to the Elemental Plane of Fire, which they did with the help of Vox Machina and Gern Blanston.

Rebuilding Pyrah
In, Cerkonos began regrowing his left arm.

Trivia

 * Cerkonos is the second character featured in Critical Role missing a hand, preceded by Anna Ripley and followed by Tyriok Gadsworth and Shale.  (Victor is missing two fingers from a hand, but he still has most of it.)