Tsathoggua is a great pale toad like creature who generally lives underground.
He (or it since its gender is a mystery) has existed since the destruction of Valusia. For some time it dwelt in the cave N'kai under Yoth or Mount Voormithadreth It is also probable that Tsathoggua or an avatar of it lived in modern day Hungary near the Black Stone.
Tsathoggua has been worshiped by a wide range of peoples. The Serpent Men took idols of Tsathoggua from N'kai. Many other cults have adopted the toad god as a symbol. Many of these cults may not know of Tsathoggua's true name and the toad symbol has become ambiguous as a symbol of evil.
The Black Stone
One possible cult of Tsathoggua in recent history is one depicted in Robert E. Howard's story The Black Stone. In Hungary the people of the village of Stregoicavar worshiped a toad god who sat atop the Black Stone.
When the Turkish armies invaded the original inhabitants where all killed off and the toad god slain in its cave. A record of the Turkish invasion survives in a lacquered case used by the Turkish scribe Selim Bahadur. The case was buried with Count Boris Vladinoff when his castle collapsed under Turkish cannons. The case was later dug out by an unnamed man in the nineteen-hundreds and thrown into the Danube. In the case was a manuscript in Turkish describing what the Turkish invaders found in the village, as well as a small gold idol depicting the toad god.
According to the Turkish description and certain visions perceived near the Black Stone on Midsummer Night the local people gave brutal ceremonies to the toad god and sacrificed infants and young girls to the actual creature that came down from the mountain.