Domains: Monstrous things, the deep, what should not be looked at.
Era of ascension: Golden Age of Man (~140,000 years ago). Cohort: dead. Died: God War & Long Winter (~75,000 years ago), when the surface-extinction of the Winter left no civilizations capable of studying the depths and his cult, which had always depended on the surface for its observers, ended.
Worshipped by: The abyssal cults of the Golden Age, deep-sea sailors whose ships went where no fleet returned reliably from, and the small temple-orders that maintained the study of what surfaced from the dark. No living culture maintains his worship. (The worships edge is authored downstream on the worshipper, not here.)
Uzdakh was worshipped with averted gaze. His rite was conducted by a single priest at a time, alone, in a chamber with no light, with the worshipper turned to face the wall and the offering placed behind them on the floor. The doctrine insisted that looking at the god directly was not blasphemy but pointlessness — what surfaced from his domain was already wrong, and the wrongness was located in the looking, so one did not look. The cult's records were therefore voice-records, dictated and never read back. The libraries kept the seals; the seals were never broken in any documented case.
His worship was sparse, durable, and confined to the coastal cities with reason to know what lived in the deep water — port temples paid by maritime guilds to keep the wrong things on their side of the surface. The God War made him strangely irrelevant: the surface was tearing itself apart and what was beneath did not care. He outlived several other Golden-Age cults that way, simply by being beneath the conflict. The Winter then killed him at a different angle: the surface civilizations that observed his domain went under entirely, and a god whose worship is the observation of the deep cannot be sustained from inside the deep. His last priests starved at empty harbours; what they were maintaining the watch on did not reach up after them.
Thaleth is the navigable ocean; Uzdakh was what was under it. Brethis is the dream you walk into; he was the one that walked into you and could not be reasoned with.