Echmínt, Echwydd
A character mentioned in the Triads, often in relation to various heroic and legendary events, but the texts do not provide extensive details about this character. Unfortunately, there is limited information available about Echymeint beyond the references found in the Triads.
I do not know if he has any connection with the Stone of Echymeint.
Source
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century