The Lord High Conservator seems to be the top official in charge of The Incorruptible Republic of the Immortal Library of the Grand Architect, usually just referred to as The Incorruptible Library, The Immortal Library, or simply as The Library. This "Library" occupies a large subterranean area off of the Paris Black Market, which has successfully asserted its independence from the Master of Paris. When he is first mentioned in the story, he is off on a raid for reasons connected with the appearance of the new type of miniature Hive Engine in Paris. Apparently, he takes a very active role in managing the Library, since the remaining officials are when he is away.
it's eventually revealed that his raid is a successful attempt to "rescue" a newly-extracted Tarvek from the "clutches" of Baron Gil on the outskirts of a time-frozen Mechanicsburg. Unfortunately, during the return journey his airship is brutally hijacked and redirected by a cadre of disguised Smoke Knights dispatched by Grandmother. He kills three of them, but is (evidently) fatally stabbed and poisoned in the process, leaving only Tarvek and Mister Obsidian alive on the airship.
The Lord High Conservator is a very imposing figure, extremely tall, strongly built, and muscular, with short blonde hair, light but slightly tanned skin, and green eyes. His eyes are his most striking feature by far, since he has four of them: two pairs, one set directly above the other. This can make his face somewhat disturbing to look at, especially when the two sets of eyes are looking in different directions.
The word "READ" appears on his left shoulder, apparently a tattoo. It is also printed on the scabbard of the enormous sword he carries on his back.