Koroth, one of the Guardians, in 2369

The Guardians were a group of Klingons associated with the monastery on Boreth, where the Followers of Kahless awaited the return of Kahless. Among them was Koroth. (TNG: "Rightful Heir")

In 2369, Kahless appeared to have returned to Boreth. Chancellor Gowron was sceptical, believing the Guardians had always opposed him, and this manifestation was an attempt by the guardians at finally seizing power over the Klingon Empire.

Shortly afterwards, The Klingon claiming to be Kahless was revealed to be a clone. (TNG: "Rightful Heir")

The time crystals present on the planet were managed by a group which called themselves the timekeepers, and described themselves as guardians, not rulers. (DIS: "Through the Valley of Shadows")

While Koroth identified himself as a Guardian, he also demonstrated knowledge about the story of the sword, which he said was only known to the High Clerics. This suggests at least some overlap between the two terms.
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